This forum is for the File Geodatabase API. ArcObjects at 10.0 and 10.1 (and of course 9.3.x)
should be able to read 9.3 FDGB data. If ArcGIS can't read your data, then this doesn't reflect
on the FGDB API, since ArcObjects uses a different library (FileGDBAPI is a port of a *part*
of the ArcObjects library). It's unlikely the FileGDB API will be able to read a 10.x dataset
that ArcGIS 10.0 cannot.
If you can't read a file geodatabase with a release of ArcGIS that should be able to read it,
then there's a good chance the data files have been corrupted. Unfortunately, your only
option is to contact Tech Support for help in data recovery. They will need a complete copy
(Zip or 7Zip) of the file geodatabase folder.
Good luck.
- V