GetDiskFragment error -2806

I have developed a JNI Mach-O library in Tiger, under CodeWarrior 8.3, that opens
dynamically a native carbonised library using FSMakeFSSpec and GetDiskFragment. In order
to test this I have created a small java program that tests the functions in the
carbonised libary. Although this worked OK, when the JNI lib is called through a big Java
client program I get an error -2806 from GetDiskFragment. Anyone knows the cause (and
possibly a solution) for this error, the Apple documentation's "A fragment's container
format is unknown" is not very explanatory for me:)

The call is:
err = GetDiskFragment(&fss, 0, kCFragGoesToEOF, fss.name, kPrivateCFragCopy, &implConn,
(Ptr*)&CFMFuncPtrIS, junkMessage);

Thx.