Layouts can be corrupted and such corruption may be tolerated by one version and/or OS and not another. I don't know if this is the case in your part, but you might try using fmp 5.5 to recover the file and then see if the recovered files convert any differently than the originals.
Thanks a ton. That worked. Opened it in FM 6, Recovered it. Then converted it again in FM 10 and the 3 layouts were there!!!