Make sure you are using the most recent version of Pro Maps for Google that is avialbedl from the download center page.
If you have a previous version, make sure to remove it from the extension manager before installing the newer one.
This can some times happen because of conflicting code on the page such as a form named directions.
Try adding a map to a new blank page, do you still have the same problem?
Can you send a copy of your page and the Google_Javascript folder so we can try to recreate the problem on our end to find the cause.