I updated the mootools files to fix the issues with the thumbnail, the issue with the error message on the test page is because you have a Install of power gallery 1.0.0 that has an incomplete upgrade to power gallery 1.2.2.
Download the Power Gallery 1.2.2 files from the download center and follow the readme file instructions for installing the update.
Better yet would be to upgrade to Power Gallery which has better support for newer browsers like IE 10
If you upgrade form v1 to v2, it;s a good idea to make a back up of the database first.