Intel Xeon Xserve and kernel panics generated by FBD memory errors–EMC’s Retrospect?

Howdy all! I'll start with this: has anybody else with Intel Xserves had problem with kernel panics due to FBD memory errors? We are on our second logic board on a less than 3 month old Intel Xserve. The first was found to reliably kernel panic with memory in slot 4 when running a Retrospect backup. Just before the logic board was replaced, the Xseve would reliably kernel panic 15 to 20 minutes into a backup. Before the logic board was replaced, we were able to run full backups provided no memory was in slot 4. 2/05/07 the Xserve experienced another FBD memory error kernel panic during a Retrospect backup. Bad RAM? Or another bad logic board? Thoughts? Thanks! -John