Sys.WebForms.PageRequestManagerServerErrorException 12031

Question

I\'m occasionaly getting the following popup from an AJAX.NET application

Sys.WebForms.PageRequestManagerServerErrorException: An Unknown error occurred while proc         


        

Answer 1

I had the following error happening on postback:

Error: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server.

But for me, the issue was that I am converting my project from ASP.NET 2.0 to ASP.NET 4.0 and I had used on the page.

I took off the (for the time being), then ran the page to get the exact error. Which was "A potentially dangerous Request.Form value was detected"

I found that even though I have ValidateRequest="false" on the page, ASP.NET 4.0 requires you to add requestValidationMode="2.0" in the HttpRuntime tag of web.config.

Reference