Just updated our 7.2 site to 7.3. The upgrade seemed to go okay, and the site is running. However, whenever I log in, as soon as I move to another page, try to go into edit mode, or do anything else that causes a post/postback, I'm logged out again.

The result is that I am unable to edit the site, and unable to get to any settings that might fix this. 

We are using the DNN Auth Ad plugin on CodePlex, however, this also happens for the host account!

How can I fix this?