Build Queue never starts with Snapshot Dependencies configured

I have two builds: C and V.  Build V has a snapshot dependency on build C.  Both builds start fine without the snapshot dependency configured; however, once I enable the snapshot dependency, both builds sit in the queue forever, with 2 available build agents.  See attached image.

I've tried this setup in TeamCity 6.5.3, 6.5.4 and 6.5.6, but I've never been able to get it to work.  How can I troubleshoot this?

We're using ClearCase VCS.

Thanks,
Bryan