How do I allow programs that generate "high" or "severe" alerts in MS Security Essentials?

Reinstalling the program solved the issue.

I also had this issue, but after changing each default action to "recomended action" (also made sure that the box to auto perform default actions was unchecked).

STILL no "allow". BUT, if you CHECK THE BOX next to the item in quarantine, THEN you can allow it.

I was very frustrated until I checked the box!