>>Do you use any plugins that change the behaviour of the editor?

I have kimli flash embedder - but I tried deactivating it and nothing changed.

>>Do you use any content filter (antivirus software/spyware)?

I have Kaspersky running on the computer, but I wasn't told it blocked anything, and all the other popups are working fine.

>>Just for some testing, could you install the plugin "TinyCode" and try it? there i use another way to load the tinyMCE-Plugin.

Installed, and it works just fine. The TinyCode button launches....