We upgraded our site from Omeka 1.0 to 1.2.1 today, and upgraded Exhibit Builder up to 0.5.2, as well. The site seems to be working fine for the most part. However, we are having a problem with Exhibit Builder now. When I go in to create or edit a page in Exhibit Builder, I get Error 500 in a pop up window, and am unable to add or edit images on the page template. Editing at the exhibit or section level seems to work fine. We did not have any problems with Exhibit Builder prior to upgrading.
Could this be an Apache issue? Is there anything we should look for in this .htaccess file?

