Errors

Symptoms: When you try to access your template admin pages within Drupal (/admin/themes) you get a blank page.

Under "administer » logs" you might see the error:
call_user_func(Copy of phptemplate_templates): First argument is expected to be a valid callback in E:\DomZeus\wwwroot\modules\system.module on line 572.
 

You basically have a field or fields on your node that do not update. In my case it was the Meta Tags field not being saved.

You just upgraded to php 5.2.0. You can login to your Drupal site but as soon as you click a link, like "administer", you are logged out and receive the message:

"Access denied
You are not authorized to access this page."

The following solution is verified on Drupal 4.7.4 please adjust to your version of Drupal. The solution consist of adding a few lines of code in one file and removing a few lines of code in another. Remember to make a backup copy of these files before you make the 2 following modifications.