Backup Central

I have a Dell TL4000 and I use CA Arcserv for my backups, now the thing is that inside the Arcserv softeware under the DEVICE option I see 4 drives but can only add 2 drives under my library and if i go to DEVICE CONFIGURATION and follow the steps to manually add the remaining 2 left over drives I get an error saying "Failed the assign drives the maximum number of drives have been reached" nut until yesterday I was able to see all of my 4 drives under the Library.

Also on the front LCD panel of the TL400 I see a warning for Drive 3 and 4

Any ideads how I can re-add my 2 drives to the Library in ArcServ??
I have the Tape Library option installed, I mean this Library was working fine until yesterday...

Are you licensed to use 4 drives in Arcserve?
If I recall if you plan to use multiplexing or multi stream, you need the enterprise license.