So. Problem solved after a long try and error session:

 

I have a hidden element called "action" in my existing page. Can it be, that the AjaxUploader generate a element with this name too? Because after remove my hidden action element, all works fine.

 

I think it's a good idea, if you create a list with forbidden names in the documentation to prevent such things in future.

 

But maybe you can help on some other questions:

1.

I found the Attribute "CancelAllMsg" to set the value of the Cancel-All-Button, but the Attribute "CancelUploadMsg" has no effect to the Cancel-Button. (I have no Buttons in my code, the buttons are generated by you). Whats wrong? Better is, if I can suppress all Cancel-Buttons.

 

2.

How I can remove the table with the filenames from server side after upload all files are complete?