Which release do you have and what's the script you are using? Unfortunately this message is sometimes misleading. So it could be a simple timeout or a broken script because of any change on that site.
In order to achieve what is possible, you have to try the impossible over and over again. Hermann Hesse
Do you have changed the script with your personal API-key? If you don't have please change it. There are 2 positions in this script that must be changed from /APIKEY/ to /.../ You also can use a little tool for changing it: http://www.mediafire.com/?fc9fhgd33xrod05 (in the case it is not already in your XMM's program folder. I just have tested this script with the movie Frogs (1972) and it worked fine.
In order to achieve what is possible, you have to try the impossible over and over again. Hermann Hesse
You can update as much as you want. Just select the movies and use the popup menu "Update Selected" of simply start the update wizard and chose from there all wanted movies. But attention: you can't mix the update for movies and tv shows. That needs two separated steps.
In order to achieve what is possible, you have to try the impossible over and over again. Hermann Hesse