iPod skips some mp3s synced with songbird

I few songs/albums that play perfectly on songbird (windows) and anyother music player are not playing at all on my iPod 6th gen 80gb.

The songs try to start at 0:00 then it skips to the next one, like it was incompatible. I tried adding the album/songs to itunes and itunes won't pickup the mp3s for whatever reason.

I wanted to know if this was a known problem with ipods and if anyone knew how to get these albums to be playable on it, either by using a plugin to convert on the fly (I think itunes has this feature) or something.

I don't know how to figure out if the mp3s are VBR, however ipods shouldn't have a problem with VBR as they are supposedly "supported"

Thanks