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

In our case the issue was caused by a rewriting proxy on the way. The rewrite modified the content of the update panel response. But this response also contains original size. The rewriting mechanism cannot know that few bytes of the response actually contains original response size and it should also be modified.

The update panel response starts like this:

1|#||4|30502|updatePanel|pnlUpdate| ...

The 30502 is original size of the content which is being updated. Rewriting engine modifies the output, but the size stays unchanged => parser error exception.

I don't see a way how to overcome this issue from the client side. We would need to know how exactly was the content modified and then somehow change the size in the response before UpdatePanel ClientScript starts processing it.