this worked for me
1. start diablo and make sure you uncheck "remember my log in name"
2. exit diablo completely.
3. restart diablo and verify that your log in name is not there any longer. if it is exit again and restart until it is not there.
4. alt-tab from Diablo 3 and open task manager
5. Right click Agent.exe*32 - open file location
6. In the directory go to Battle.net
7. where there are 3 folders (agent, client, setup)
8. Delete agent folder (you may get an error saying the file is in use. If so make sure you exit diablo and keep trying for a few seconds and it should eventually allow it to be deleted)
9. Run DIablo 3 again and it should patch a new agent folder in
10. restart diablo as normal

These were the exact steps i took to resolve this issue
Hope it works for others.

- good luck and cheers