My problem is, that I have the main category for my events and another category for trainers. Now I want the user to be able to just see the events for category1 from trainer1 without creating a template for each event and trainer. If set the $showcat=11 (select Trainer1) in my template, every other showcat call is ignored.
Your template will override any URL variables. You should send them via the URL only.
Ok, but why does this : www.mycalendar.de/calendar.php?showcat=11|12|&mo=6 (Filter from event mananger) not work ? Is there another way to pass the advanced filter via URL ?