I am sure most of us have come across the below error few times and Google search has provided a lot of suggestions to resolve this issue :). However, when working on one of the client's site none of the suggestions seems to have work. The error occurred when saving the page settings, creating new pages even trying to save a blank page with default skin would not work. In short they were not able to do any page management on their site.
"Uncaught Sys.WebForms.PageRequestManagerParserErrorException: Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled. Details: Error parsing near '
The error can occur due to number of things e.g. an unclosed tag (particuaraly a FORM tag), or some other piece of content that cannot be encoded, or the number of parameters.
In this case there were large number of child pages under one parent that was causing it and producing more than 1000 parameters. The number of parameters can be seen using fiddler.
Thanks to Cathal Connolly who pointed me to one of the Microsoft security update MS11-100 that restricts the amount of parameter for a single HTTP POST to 1000 see here
As suggested in the article, you can increase the parameter count by adding the below line in <appSettings> section increasing the parameter count to required.
<add key="aspnet:MaxHttpCollectionKeys" value="2000"/>
After increasing parameter count things worked as expected.
I hope this helps someone else out there too!