Yes, I read that post and have to say that its nice written, but it does not solve my popup problem. It must be the index.php from my template, cause when I open demo file, everything wirks fine. When I use the above instructions and insert the module into an article, it works... and I even tried a wrapped article that worked. The problem is that I need the calendar in a module and inserting articles inside of modules is something I haven't found yet.
I think that maybe it's best to search for a compatible template. Thanks a lot 4 your efford.