It looks like you were running an older version of powerstore that has issues in some more recent browser updates.
I fixed the problem by updating the files:
/webassist/themes/theme_close.php
/scripts/mootools-more.js
/js/mootools-more.js
and getting the latest versions from the most recent powerstore files.
(note: I replaced the /scripts/mootools-more.js file with the same file from /js/mootools-more.js since that file doesn't exist in both locations in the newer version)