foobar gave me this error, while masstagging a group of .MP4 files.
i couldn't identify exact conditions, as this doesn't happen while tagging single files, but when tagging multiple files.

system:
Windows XP Pro/Athlon XP/512 Mb.




Illegal operation:
Code: C0000005h, flags: 00000000h, address: 7C921E58h
Access violation, operation: read, address: 6E755F6Eh
Call path:
masstagger_dialog::threadfunc
This is the first crash logged by this instance.
Code bytes (7C921E58h):
7C921E18h: 89 5F 4C EB 8F 33 C9 E9 37 FF FF FF FF 75 10 57
7C921E28h: 56 E8 26 FD FF FF EB AE 0F B7 06 8B 4D 10 03 01
7C921E38h: 3D 00 FE 00 00 0F 87 EE ED FF FF 80 7D 14 00 0F
7C921E48h: 85 97 7A 03 00 8B 4E 0C 8D 46 08 8B 10 89 4D 08
7C921E58h: 8B 09 3B 4A 04 89 55 0C 0F 85 9D 00 00 00 3B C8
7C921E68h: 0F 85 95 00 00 00 56 53 E8 1F ED FF FF 8B 45 0C
7C921E78h: 8B 4D 08 3B C1 89 01 89 48 04 74 49 8A 46 05 A8
7C921E88h: 04 0F 85 2F 7B 03 00 8A 47 05 24 10 A8 10 88 46
Stack (0128FDD0h):
0128FDB0h: DCBAABCD 00000000 0012F934 773C8B56
0128FDC0h: 0012F960 77D187EB 7FFDE000 0012F960
0128FDD0h: 00890000 00CE0BA0 00000000 0128FEB0
0128FDE0h: 7C920D5C 6E755F6E 00CE0BA0 0128FE94
0128FDF0h: 00000000 77BFC21B 00CE0BA8 00000004
0128FE00h: 00E60000 00CE16F8 00000003 0128FDF8
0128FE10h: 0128FFDC 77C05C94 77BE2088 FFFFFFFF
0128FE20h: 77BFC3CE 0000001F 0000001E 004012D5
0128FE30h: 0089D078 0128FEA4 00000010 00402BD3
0128FE40h: 0089D078 0128FEA4 00CD88EC 0044559C
0128FE50h: 00000018 0000001E 0128FE6C 00000010
0128FE60h: 004012C6 0128FEA4 0128FE74 0128FEBC
0128FE70h: 00401277 0000001E 00890000 7C8024B7
0128FE80h: 00000044 00890000 00000000 00000000
0128FE90h: 01010044 00000003 0128FDF4 0128F9F4
0128FEA0h: 0128FEE8 7C91EE18 7C920570 00000001
0128FEB0h: 0128FEF8 77BFC2DE 00890000 00000000
0128FEC0h: 00CE0BA8 77BFC21B 00CE0BA8 00000004
0128FED0h: 0128FF80 00000008 00000003 00000000
0128FEE0h: 0128FEC4 0128F9F4 0128FFDC 77C05C94
Registers:
EAX: 00CE09F8, EBX: 00890000, ECX: 6E755F6E, EDX: 69616733
ESI: 00CE09F0, EDI: 00CE0BA0, EBP: 0128FDDC, ESP: 0128FDD0
Crash location: "ntdll", loaded at 7C910000h - 7C9C6000h
Symbol: "RtlInitializeCriticalSection" (+0000032Bh)

Loaded modules:
foobar2000 loaded at 00400000h - 00452000h
ntdll loaded at 7C910000h - 7C9C6000h
kernel32 loaded at 7C800000h - 7C8FF000h
USER32 loaded at 77D10000h - 77DA0000h
GDI32 loaded at 77E40000h - 77E86000h
ole32 loaded at 774B0000h - 775EC000h
msvcrt loaded at 77BE0000h - 77C38000h
ADVAPI32 loaded at 77F40000h - 77FEB000h
RPCRT4 loaded at 77DA0000h - 77E31000h
COMCTL32 loaded at 773A0000h - 774A2000h
SHLWAPI loaded at 77E90000h - 77F06000h
utf8api loaded at 10000000h - 1000D000h
comdlg32 loaded at 76360000h - 763AA000h
SHELL32 loaded at 7C9D0000h - 7D1EB000h
foo_abx loaded at 008D0000h - 008DC000h
foo_ape loaded at 008E0000h - 008FF000h
foo_clienc loaded at 00900000h - 0090B000h
foo_console loaded at 00910000h - 00917000h
foo_diskwriter loaded at 00920000h - 00932000h
WINMM loaded at 76B00000h - 76B2E000h
foo_dynamics loaded at 009C0000h - 009C7000h
foo_flac loaded at 009D0000h - 009EC000h
foo_id3v2 loaded at 009F0000h - 00A20000h
MSVCP60 loaded at 76030000h - 76095000h
foo_input_std loaded at 00A20000h - 00ABE000h
MSACM32 loaded at 77BB0000h - 77BC5000h
foo_masstag loaded at 00AC0000h - 00AD4000h
foo_output_std loaded at 00AE0000h - 00AE9000h
foo_rgscan loaded at 00AF0000h - 00AFD000h
foo_ui_columns loaded at 00B00000h - 00B2F000h
foo_ui_std loaded at 00B30000h - 00B47000h
foo_vis_manager loaded at 00B50000h - 00B58000h
foo_wma loaded at 00B60000h - 00B7A000h
WMVCore loaded at 7D7A0000h - 7D9AA000h
wmidx loaded at 4B360000h - 4B389000h
WMASF loaded at 59E10000h - 59E4C000h
OLEAUT32 loaded at 770F0000h - 7717C000h
msdmo loaded at 73620000h - 73627000h
WININET loaded at 77180000h - 77227000h
CRYPT32 loaded at 77A50000h - 77AE5000h
MSASN1 loaded at 77AF0000h - 77B02000h
urlmon loaded at 77230000h - 772CD000h
VERSION loaded at 77BD0000h - 77BD8000h
MSVFW32 loaded at 75DF0000h - 75E11000h
WSOCK32 loaded at 71A50000h - 71A5A000h
WS2_32 loaded at 71A30000h - 71A47000h
WS2HELP loaded at 71A20000h - 71A28000h
DRMClien loaded at 00B80000h - 00BCF000h
UxTheme loaded at 5B180000h - 5B1B8000h
appHelp loaded at 77B10000h - 77B32000h
CLBCATQ loaded at 76F90000h - 7700F000h
COMRes loaded at 77010000h - 770E2000h
cscui loaded at 779F0000h - 77A45000h
CSCDLL loaded at 765B0000h - 765CD000h
netapi32 loaded at 5BC70000h - 5BCC4000h
USERENV loaded at 76980000h - 76A34000h
MPR loaded at 71AA0000h - 71AB2000h
drprov loaded at 75F10000h - 75F17000h
ntlanman loaded at 71BA0000h - 71BAE000h
NETUI0 loaded at 71C60000h - 71C77000h
NETUI1 loaded at 71C20000h - 71C60000h
NETRAP loaded at 71C10000h - 71C17000h
SAMLIB loaded at 71B80000h - 71B93000h
davclnt loaded at 75F20000h - 75F29000h
SETUPAPI loaded at 778F0000h - 779E7000h
wiashext loaded at 4EE60000h - 4EEF3000h
gdiplus loaded at 4EBD0000h - 4ED73000h
xpsp2res loaded at 20000000h - 202D5000h
sti loaded at 73B10000h - 73B24000h
CFGMGR32 loaded at 74A70000h - 74A77000h
imagehlp loaded at 76C50000h - 76C78000h
DBGHELP loaded at 59E60000h - 59F01000h

Stack dump analysis:
Address: 7C920D5Ch, location: "ntdll", loaded at 7C910000h - 7C9C6000h
Symbol: "wcsncpy" (+000002CDh)
Address: 77BFC21Bh, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "free" (+00000000h)
Address: 77C05C94h, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "except_handler3" (+00000000h)
Address: 77BE2088h, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "__non_rtti_object::`vftable'" (+00000C90h)
Address: 77BFC3CEh, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "free" (+000001B3h)
Address: 004012D5h, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 00402BD3h, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 0044559Ch, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 004012C6h, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 00401277h, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 7C8024B7h, location: "kernel32", loaded at 7C800000h - 7C8FF000h
Symbol: "ReleaseMutex" (+00000010h)
Address: 7C91EE18h, location: "ntdll", loaded at 7C910000h - 7C9C6000h
Symbol: "strchr" (+00000117h)
Address: 7C920570h, location: "ntdll", loaded at 7C910000h - 7C9C6000h
Symbol: "RtlFreeHeap" (+00000133h)
Address: 77BFC2DEh, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "free" (+000000C3h)
Address: 77BFC21Bh, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "free" (+00000000h)
Address: 77C05C94h, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "except_handler3" (+00000000h)
Address: 77BE2070h, location: "msvcrt", loaded at 77BE0000h - 77C38000h
Symbol: "__non_rtti_object::`vftable'" (+00000C78h)
Address: 00AC46BCh, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00AC466Ch, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACC21Ch, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00AC4614h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 10002E5Dh, location: "utf8api", loaded at 10000000h - 1000D000h
Symbol: "uPostMessage" (+00000000h)
Address: 00AC4F64h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACC9F0h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACCA64h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACCA5Ch, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACCA48h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACCA5Ch, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00ACCA48h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00AC6267h, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 7C80B50Bh, location: "kernel32", loaded at 7C800000h - 7C8FF000h
Symbol: "GetModuleFileNameA" (+000001B4h)
Address: 7C8399F3h, location: "kernel32", loaded at 7C800000h - 7C8FF000h
Symbol: "FindAtomW" (+00000094h)
Address: 7C80B518h, location: "kernel32", loaded at 7C800000h - 7C8FF000h
Symbol: "GetModuleFileNameA" (+000001C1h)
Address: 00AC625Eh, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 004210ADh, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 00444709h, location: "foobar2000", loaded at 00400000h - 00452000h
Address: 00901180h, location: "foo_clienc", loaded at 00900000h - 0090B000h
Address: 00928D20h, location: "foo_diskwriter", loaded at 00920000h - 00932000h
Address: 009D955Bh, location: "foo_flac", loaded at 009D0000h - 009EC000h
Address: 009FE1B4h, location: "foo_id3v2", loaded at 009F0000h - 00A20000h
Address: 00A233E9h, location: "foo_input_std", loaded at 00A20000h - 00ABE000h
Address: 00A43C2Bh, location: "foo_input_std", loaded at 00A20000h - 00ABE000h
Address: 00A627C9h, location: "foo_input_std", loaded at 00A20000h - 00ABE000h
Address: 00A7E29Eh, location: "foo_input_std", loaded at 00A20000h - 00ABE000h
Address: 00AA0C3Fh, location: "foo_input_std", loaded at 00A20000h - 00ABE000h
Address: 00AC9B7Bh, location: "foo_masstag", loaded at 00AC0000h - 00AD4000h
Address: 00AF2C47h, location: "foo_rgscan", loaded at 00AF0000h - 00AFD000h
Address: 00B1B630h, location: "foo_ui_columns", loaded at 00B00000h - 00B2F000h
Address: 00B425FEh, location: "foo_ui_std", loaded at 00B30000h - 00B47000h
Address: 00B6A0C6h, location: "foo_wma", loaded at 00B60000h - 00B7A000h
Address: 00B9354Ah, location: "DRMClien", loaded at 00B80000h - 00BCF000h
Symbol: "DllUnregisterServer" (+00000A8Ah)
Address: 00BBCB23h, location: "DRMClien", loaded at 00B80000h - 00BCF000h

Version info:
foobar2000 v0.8.3
UNICODE