JavaScript error in with IE10 with ImageButton in UpdatePanel

Hello,

I have a JavaScript error using an ImageButton inside an UpdatePanel:

- create new empty webside in VS2012
- create new webpage
- put ScriptManager on the new webpage
- put an UpdatePanel on the page
- put an ImageButton inside the UpdatePanel
- write some code for the onclick-Event of the ImageButton

Start application, click on the ImageButton and I get an error message:
Runtimeerror in JavaScript: Sys.WebForms.PageRequestManagerServerErrorException: Input string has wrong format.

This happens only with IE10, not in compatibilty mode, nor in IE9,..., Chrome, Firefox; it does not happen if the ImageButton is outside the UpdatePanel.

Any ideas?

Thanks for any help!
Roger