My website's front-end shows up fine. I can navigate the pages submit forms. From the moment I try to login with a user, I get DNN Error with a "Return to Site" link that just bring me back to the same exact page.
I have not installed any new modules on the website, or changed skins, or modified the DLL's in any way, which is what's really strange.
The logs on the SQL "EventLogs" table just show a very simple error message that is no help at all.
Reviewing the log files in the root directory I did find a more informative error message and have posted it as a comment to this post.
My IIS Settings/APP pool Settings have not changed still running asp.net 4.0 and the web.config connection string to my DB is still correct. I've no clue what's happening. I'd really appreciate some insight should anyone have an idea.