Ok, some questions:

1 - What are the SIZE of the database file (turn off the server
or do not allow anyone to connect)?

FAT32 on Win98 have a 2Gb limit on file size. It can go to 4Gb
on the WinNT/2k systems. Don't know what are the limit of NTFS,
but is much bigger as it uses 64bit I/O.

AFAIR, Ib6 cannot address more than 4Gb; any database that reach that
point, and grow, is corrupted.

2 - Do you have enough disk space free to run the backup operation?

3 - I don't know Firebird (I think it even don't allow), but Interbase
allowed someone to create databases on W9x systems that runs on with
ForcedWrites OFF. Although it can speed things, it's completely insane
the
corruption risk someone takes doing such a thing... Do you did that?

>I don't need coments "you should use linux, it is more stable", I
>need help to solve the problem.

Don't say Linux, but anything is better than W98...