greattraders

I'm on the free trial of CA ARCserve Backup r16. After coming from Backup Exec, I'm not finding it easy.
How do you set it up to do a series of GFS backup jobs to disk.
At the moment, it runs the first backup job OK, and creates a set of files on the NAS in the format S0000001.ctf. OK so far.
All the subsequent backups fail. It asks for a new media, like it thinks the NAS is a tape drive. I get 'Please mount media in the device group GROUP1'.
How do I tell it that the target is a NAS and that it should create new files as it needs to. Backup Exec used to do this no problem?
CA's support website is no use.
Thanks.