Is there a question mark visible in the status bar at the bottom of the window? If there is, there might be an issue with the overwrite status of the media. Click the question mark and choose to overwrite the media.
Try clearing alerts as well if you have a lot of them.
I used to get this problem with version 9 frequently. With that I usually had to stop the services, wait a while and restart them.
You might have also be having an issue with the device itself. Check that the device can be seen and selected. Backup exec might not be recognising it and holding the jobs as a result.