I had this one reported to me recently, and I thought I should contribute to public knowledge on it.

THe problem was that a site running Url Master and the Telerik Rad Upload control would fail whenever the upload size was larger than 130kb.   I immediately thought of the similar problem that was occuring with the NeatUpload control - which does a similar thing in that it provides a progress update bar.

That problem (with NeatUpload) was found by someone using both Url Master and Snapsis Pageblaster on a site, but the problem turned out to be related to the NeatUpload component.  The resolution turned out to be that moving the NeatUpload <httpModule> entry to the top of the list of httpModules fixed the problem.

So on a hunch, I asked the person with the problem to move the Telerik Rad Upload Control (incorporating the Rad Progress Mgr and Rad Progress Bar) to the top of the list of httpModules in the web.config - and this fixed the problem.  I'm guessing it was the same problem:  The progress bar does something by reading the request - and if the Url Master module reads that request *before* the upload control,  it flushes out the request data and the upload control fails.  This was the same error as with Neat Upload.  The Url Master module reads the request.params collection, which is what causes the problem. 

Incidentally, you can set a web.config attribute of the Url Master module called "allowDebug='false'" which stops it from reading the request params collection.

Also, if you're running Snapsis Page Blaster and Telerik Rad Uploader, I bet you get the same problem, with the same solution : move the httpModule entry to the top of the list.