OSX Mountain Lion logs out after login

Solution 1:

Make sure you dont have Log-In options enabled. If they are, disable them. It sounds like you might be running a Log-In option.

Check out this link to learn more about Log-In options.

http://support.apple.com/kb/PH10650?viewlocale=en_US

EDIT: Since you don't have any log in options enabled, it sounds like it might just be a lag from the screen waking up.

Does this happen when you are attached to an external monitor as well? Or does it only occur when you open the lid?