FSBTool ERROR: Cannot encode file, source format (PCM 32bit) is unsupported.

In June/July next year we are to jump to the Pro version after we have completed all the conversions and got things stabilized. But we are running into a multitude of problems... one of wich is:

migrated to 5.xxxx from 4.xxxx - .wav files fail import(or Unity scrutiny if it is not the import) - sounds in game are dead.

Can anyone give me at least a clue! as to what approach to take? I hope having to regenerate these sounds thru the Unity Recording mechanism is NOT the only option! That would mean massive time cost! Thank you for any clues!