Why am I not getting any Work Units

The easiest possibility is that nothing is wrong--just your boincmgr thinks you have done enough Einstein for the moment and is not requesting any more until your other projects get into good enough share balance at it sees it.

Have you looked at the message log to see whether your PC is making requests of Einstein? You are running 7.0.28, so this would mean Advanced|Event Log, then scrolling through.

In that format, here is a successful Einstein work request as seen on one of my hosts, which happened to want GPU work at this time:

7/24/2012 7:36:23 AM | Einstein@Home | Sending scheduler request: To fetch work.
7/24/2012 7:36:23 AM | Einstein@Home | Reporting 4 completed tasks, requesting new tasks for NVIDIA
7/24/2012 7:36:27 AM | Einstein@Home | Scheduler request completed: got 5 new tasks

You can also ask the Einstein server what the most recent work request for you host looks like. Here is a link for that information for your host:

host 4280432 most recent work request

At the moment I am writing this, that links shows these in these three lines that just before the end of July 24 UTC, your host requested zero work.

2012-07-24 23:31:41.4546 [PID=19584]    [send] CPU: req 0.00 sec, 0.00 instances; est delay 0.00
2012-07-24 23:31:41.4547 [PID=19584]    [send] CUDA: req 0.00 sec, 0.00 instances; est delay 0.00
2012-07-24 23:31:41.4547 [PID=19584]    [send] work_req_seconds: 0.00 secs

Others here may be better able than I to help you see better the status of the competing projects on your host.

My own recommendation is patience and watchful waiting.