Exchange Backup—GRT Processing Hangs at 0 of N backup selections

I'm running Backup Exec 2014, and backing up an Exchange 2007 server. For a good amount of time, everything was going well. Recently, however, after a change to one of the storage groups (Disabling circular logging), the job hangs immediately after GRT processing begins. The latest job has gone for 36 hours without processing any Storage Groups for GRT data. The backup, itself, is only taking about four hours.

Any thoughts on what will cause this, or what debugging I could turn up to get more information?

Thanks,
Brian