[Plugin: WP Opt-in] Inserting media error [Are you sure you want to do this?]

When the opt-in plug-in is activated I cannot add any media to my posts. When I click on upload/insert the screen that pops up says, “Are you sure you want to do this? Please try again.” When you click that link, it goes to a smaller version of the post you’re already looking at, but still gives you no alternate option to upload anything.

I have had this problem in both Firefox and IE.
FF version v.3.6.16

IE version 8.0.6001.18702

WordPress version 3.1.1