Have you looked at the tomcat output and server output to see if it specifies an error there?
Oh, and a picture might not hurt. You talk about a Calendar and a presentation, and I have absolutely no clue what you’re talking about. And you ended with “query presentation”, which doesn’t mean anything to me either.
I’ve recently done lots of work with the scheduler, accessing it from a content panel in a VP. And I’ve added and edited events just fine, so I think we’re doing similar things, but in totally different ways.