Test restore jobs have started failing.

I've had several scheduled jobs running for months to do a weekly test restore and run DBCC checks on the restored db's. In the last two weeks the jobs have all started failing with this error message:

SQL Backup failed with exit code: 790 SQL error code: 3257 [SQLSTATE 42000] (Error 50000). The step failed.

SQL Backup 7.0.3.2 is installed, I"m updating that to 7.3 right now.

SQL Backup is installed on a Windows Server 2008 VM running on an ESX host (servername = PLUTO). SQL Server 2008 R2 is installed there, also. It manages backups on three SQL servers on the network (srvernames MARS, UTAH and SONORA). Everything is SQL Server 2008 R2. All backups are done locally to their resident servers, then archive copies are copied to three other locations, one off site. The job that were working fine restored the latest backup from four enterprise critical apps (2 on SONORA and 2 on MARS) to the SQL Server instance on PLUTO, the server that hosts SQL Backup. The successful backups then ran the full set of DBCC checks.

The SQL Backup log files I can find are empty, but I don't find them at exactly the path specified in the docco. Where should the logs be on a Windows Server 2008 R2 64-bit machine?