Some of the AJAX Scroller users might have noticed problems with recently released Internet Explorer 9. The issue is manifested in AJAX Scroller not working in IE9 for Joomla 1.5 sites with activated Mootools upgrade plugin. Read on to see how to fix this.

IE9 will show you a JS error "DOM Exception: INVALID_CHARACTER_ERR (5) mootools.js". The error is caused by Mootools 1.2.4 included in Joomla 1.5 Mootools upgrade plugin (up to the latest Joomla 1.5 revision, which is 1.5.23 in the moment of writing this post). Mootools 1.12 version included in Joomla default installation is not affected. Fixing the issue There are 2 ways to fix this problem:

1. Turn off the Mootools upgrade plugin. If your other modules or templates don't require extra features of Mootools 1.2 the easiest way for you to fix this issue is to turn off the Mootools upgrade system plugin. This will downgrade you to default Mootools 1.12 which works just fine with IE9. To do this go to Joomla admin > Extensions > Plugin Manager > Select Type > system. Find "System - Mootools Upgrade" on the list and disable it.
2. Upgrade to Mootools 1.2.5 If you do require Mootools 1.2 you will need to upgrade to 1.2.5 to fix the issue with IE9. Download the new mootools.js file here, unzip and upload it to ./plugins/system/mtupgrade/

Thanks to ghazal for the fixed Mootools 1.2.5 package for Joomla 1.5.