backup exec suddenly wont overwrite tapes

hoping someone can help me. phone support has not really helped me out

I run a nightly job to an lto 4 tape. the tape has a capacity of 1.6tb compressed. the job is only 600gb

this job has worked without any problems since we set it up months ago. suddenly im getting a promtp each night to insert overwritable media.

the majority of my media set is already overwriteable as you can see

each night the only thing i can do to get the job working is to move the tape to scratch and then it will run

i have to do this each night (even weekends) when we dont do tape changes and im getting sick of it.

any advice would be greatly apprecaited

michael