Save failed with the following error: Null primary key not allowed

While saving an article, you encounter this error message "Save failed with the following error: Null primary key not allowed".

This error message indicates that the changes cannot be saved.

Problem with #__assets table

1 of the causes of this problem may have to do with the assets table added in Joomla 1.6.

To fix this you need to go through the following 3 steps.

1. Go to Menus > all menu items. Click on the "Rebuild" button.
2. Go to Content > Categories. Click the "Rebuild" button.
3. Go to Content > Articles. Select all articles. Click the "Rebuild" button.

Problem with a plugin

Another cause of this problem may lie in 1 of the plugins you have installed. Chances are it is a plugin in the category "content" or "system".

Go to Extensions > Plugin Manager and filter the plugins by Content (or System).

After this, disable and re-enable the plugins 1 by 1 to find out which plugin is causing the problem.

Once you find the plugin, contact the developer to fix the problem.