Issue with mount request for the library manager

Hi

Here is our situation:

TSM servers 5.5.5.0
Library manager 6.3.1.0

We are having problems with mount requests. If a TSM operation needs a tape to be mounted in the library and is not in the library, we use to have a certain time to mount the tape in the library. Now , we get this message ANR9790W because it can't find the tape in the library and puts the tape to unavailable.

Can someone help me please

Thanks