AD Import not working

I just noticed that our AD import for computers isn't working at all - only about 50 computers out of 800 or so have imported, despite a manual run showing as completed successfully. I checked the logs and the general results are:

- Found and processed 66 OU's OK (and they exist)

- Found and processed 879 computer resources - says 100% complete but they don't exist.

Immediately afterwards, there is an error like this:

EventRouter could not deliver the following file..

ServerBusyException: Queue was full

Everything else seems to be working OK. Could the error be related?