(This is just for my own reference as i’ve hit this twice now – and can never find anything on google). if you run Drupal on a non standard port (e.g. on my windows machine I run apache on port 6060 so it doesn’t clash with port 80 hog IIS), you may find that you can’t log into a drupal site. This may be because of the way cookies are set up for domains. You can get round it by going to settings.php and looking for the section that is preceded by the comment:
* We try to set the correct cookie domain. If you are experiencing problems
* try commenting out the code below or specifying the cookie domain by hand.