access denied when viewing profiles of other users
Impossible to say exactly without having access to your site, but something ON the profile page is causing this.

Do this (assuming you're on Drupal 7):


Open /modules/user/user.module
Scroll down to line 820 (which should be: return isset($perm[$account-&gt;uid][$string]);)
Immediately above that line, add this code:


.

if (!isset($perm[$account-&gt;uid][$string])) {
  echo 'denied permission: ' . $string . '&lt;br/&gt;';
}



Reload the page as a user that's getting Access Denied, and you'll get a printout of all permissions the current user got denied - one (or more) of them will be the culprit. 


Don't forget to remove the code changes once you've found the issue.