Here goes description.

File naming scheme: ANSI artist/date — album/nn.title
Format string: $caps2($ansi([%artist%/][%date% — ]%album%/$num(%tracknumber%,2). %title%))
Preview: Wisp/2003 — Frozen Days/01. White Out

And the preview given in the "Rename, move or copy files" dialog:
[SYNTAX ERROR IN FORMATTING STRING]/[SYNTAX ERROR IN FORMATTING STRING]/01. white out[SYNTAX ERROR IN FORMATTING STRING].mp3

The same situation with:
File naming scheme: ANSI artist or album artist/date — album/nn.title
Format string: $caps($ansi([$if($meta(album artist),$meta(album artist)/,$meta(artist)/)][%date% — ]%album%/$num(%tracknumber%,2). %title%))
Preview: Wisp/2003 — Frozen Days/01. White Out

Preview given in the "Rename, move or copy files" dialog:
[SYNTAX ERROR IN FORMATTING STRING]/,wisp/[SYNTAX ERROR IN FORMATTING STRING]/01. white out[SYNTAX ERROR IN FORMATTING STRING].mp3

Problem persists with
$caps2($ansi([%date% — ]%album%/$num(%tracknumber%,2). %title%)) and
$caps2([%date% — ]$ansi(%album%)\$ansi($num(%tracknumber%,2)).$ansi(%title%)) constructions but ceases with
[%date% — ]$ansi(%album%)\$num(%tracknumber%,2).$ansi(%title%) string.

Result of 30 minutes of experiments:
$ansi() and $caps/$caps2() combined with any if construction ($if/$if2/[]) gives syntax errors in result. In my case it is artist tag availability check.

Foobar version 0.8.3
Masstagger version 1.4.5

Masstagger for foobar2000 v0.8.3 splits formatting strings at \ and / characters before evaluating them. This problem and possible solutions have been discussed multiple times already, so you should be able to find more information if necessary.

Thank you.