The message didn’t give many clues about the source. I noticed some HTML from the infoWindow. Are you using a customized ‘map_poi.php’ file? There could be some code conflict there.
Here are some other things to try:
1) Check your PHP and Apache error logs to see what the original error was
2) AJAX errors are often caused by another plugin or theme – try deactivating ALL other plugins and switching to a standard theme for a moment and see if the error persists.
If that doesn’t help, please reactivate the latest version and send me an admin login using the contact form, and I can try to trace it for you.