I have some mp3 ripped with an old version of musicmatch jukebox (v.5) that shows "first frame missing" in mp3trim 1.90, the question is do I've to fix this issue with mp3trim or leave it?

Thanks in advance for any help.

It is "perhaps" silence from the CD gaps. Listen to the beginning of the mp3's, if you don't hear any problems there's no need to try to fix anything. mp3Trim even shows some missing frames (although its at the end of the file) from time to time when ran on freshly encoded mp3's using LAME, and FhG.

Like 'Andavari' mentioned listen to the beginning and see if you here something, otherwise just trim off a couple frames.

Thanks for your answers, I didn't hear anything weird at the beginning, the file appear to be normal but the mp3trim shows 0,6KB to trim

In my experience as long as you didn't change the settings haphazardly, I never
have had it damage a file. If its a repairable condition it fixes it otherwise notifies
you of the problem.
Any problems in the beginning or end are typically a piece of cake. Its the errors
inbetween that are signs of corruption and a bad encode in which you will definitely
hear some type of glitch and are unrepairable.

Thank you.

My guess is that it could possibly be some tag that written to the beginning of the file. Maybe id3v2? Either the tag got corrupt or mp3trim does not recognize it as valid data. I have had this a lot and removing the first frame has never impacted on sound qaulity for me, but I remember having some issues with Lame tag getting messed up with mp3trim. I think the lame tag is written to the beginning of the file so maybe this could be it...