Arcserve2000

With Arcserve 2000 I am trying to make a 5 days differential with GFS Enable.
I is a test computer, there no data on it, the backup take 8 minutes…
The problem is that after the first tape, it continues and remake the same backup on the 2nd, 3rd, 4th….tape.

I dont know if it is a bug of arcserve or if there is something else.
On my other servers(nt-4), I have Arcserve 6.5 and I never had such problem.

Can someone help me.