After upgrading a website from joomla 1.0.x to 1.5.x I could not create a new article or copy an existing article. The New and Copy Article buttons did not work.

This seemed to be caused by a javascript error in /includes/js/joomla.javascript.js, it could not process this statement:

document.adminForm.hidemainmenu.value=1;

It looked like something had gone wrong when transferring the files because the javascript file seemed to be the one of before the upgrade. When looking on the server it turned out that the javascript file had been correctly overwritten by its counterpart in joomla 1.5.x.

The problem was that my browser was still using a cached javascript file from before the upgrade. Joomla 1.0.x and joomla 1.5.x both use the file /includes/js/joomla.javascript.js. This old file only removed from the browser cache after pressing CTRL-SHIFT-R in Firefox 3 (or CTRL-R in IE7) in the article menu. After this page refresh the buttons were working again.