ASP.NET Ajax Error: Sys.WebForms.PageRequestManagerParserErrorException

Question

My website has been giving me intermittent errors when trying to perform any Ajax activities. The message I get is

Sys.WebForms.PageRequestManagerP         


        

Answer 1

I solved this exact same problem removing the Content-Type: form the Custom HTTP Headers section in the HTTP Headers tab in IIS. This was breaking the encoding of the page and somehow it affected Ajax in general.

The Content-Type I had configured in IIS was setting the encoding to ISO-8859-1.