I recently upgraded to WP 3.5 and found out that the Add Media button is not working in Brightbox.
I researched this forum and WordPress forum, and tried the following steps already:
Upgraded to Brightbox 1.4
Deactivated all plugins
However, if I switch to WordPress Twenty Eleven theme the Add Media button works without problems, even with all plugins activated. So I'm assuming this could be a Brightbox issue and I'm asking for help.