Hi all,
Just wanted to post this in case somebody else ran into this issue.
I installed wp8 corona cards with visual studio express 2012 for windows phone. I found that it became quite unresponsive and was running one of my cpu cores at 100%. I went to Tools->Extensions and Updates and it failed with a popup box saying it didn’t have access to the corona card extension. I reopened visual studio with admin privileges and everything worked great!