A: 

I think it has to do with ASP.NET request validation: http://www.asp.net/learn/whitepapers/request-validation/

It throws the exception if e. g. HTML tags are sent with the request.

Max
+2  A: 

Looks like you have HTML markups in the submitted form fields, could be this one:

&_TSM_Combin%20</div>%20%20%20%20%20%20%20%20<div%20id=

The <div>'s the culprit.

o.k.w
I think that would have given a "potentially dangerous Request.Form" exception. Here it is Request.RawUrl instead of Request.Form.
Ole Lynge
o.k.w
Yes. It is in the url for some script generated by asp.net. I think form fields with html would generate a "potentially dangerous Request Form" exception instead of Request.RawUrl...
Ole Lynge
@Ole: That should be the case, I guess.
o.k.w
I will downvote this one, since it seems quite misleading and not addressing the question...
Ole Lynge