This appears to be related to key exchange problems. But uninstalling and reinstalling the agent didn't help. Rebooting the core didn't help. And some of these very same tasks completed on systems this morning but are no longer completing. It's something that's happening on every Mac I have tried (both 10.8.5 and 10.9.4 versions).
The only thing I see that's coincidental is Microsoft "Patch Tuesday" patches were applied to the core last night. Anybody else seeing issues this week?
I have a case open with Support on this. I'm hoping we can figure it out...