Filegroup Backups

I'm trying to do a Full Backup on a filegroup but
everytime I try to run it I get this error:
[SQLSTATE 01000] (Message 4035) BACKUP
DATABASE...FILE=<name> successfully processed 1625664
pages in 625.900 seconds (21.277 MB/sec). [SQLSTATE 01000]
(Message 3014) The value '0' is not within range for the
FILE parameter. [SQLSTATE 42000] (Error 3250) VERIFY
DATABASE is terminating abnormally. [SQLSTATE 42000]
(Error 3013). The step failed.
Does anyone have any idea as to why this is happening?
I'm running SQL2000 on a Win2K Server. SQL Books Online
is no help.
Thanks
JeroockoAs Jasper says you need to post the command the part of
your error 'The value '0' is not within range for the
FILE parameter', usually means an error in the code, wrong
file name, running against the wrong database, something
like that.
Regards
John