Users cannot login after Upgrade to 7 I have upgraded a D6 to D7 site on my localhost. After upgrade I can login using admin credentials as per usual. I have disabled Clean URLs and I see that users are in detabase. Actually all works well however when I try to log in to a user account, I get:

The website encountered an unexpected error. Please try again later


I get this error also, when I create a user from admin panel. 
I tested a lot of suggestions but none helped. So appreciate your hints.
To figure out what was the problem, thanks to this post I opened include/error.inc

and replaced

print theme('maintenance_page', array('content' =&gt; t('The website encountered an unexpected error. Please try again later.')));


with 

print theme('maintenance_page', array('content' =&gt; t('The website encountered an unexpected error. Please try again later.'.$fatal.' '.var_export($error,true))));


The new command prints out some useful info that can be used to debug. In my case, it turned out that messaging module caused the problem. I disabled messaging, and could login afterwards.

Note: before going to production, switch back to original error.inc, since the error outputs can be a gift to attackers.