Sys.WebForms.PageRequestManagerParserErrorException occurs only for two dealers (Internet explorer)

Here is the scenario: We have multiple clients,dealers and staff in our application. this problem occurs only at dealer's area. and it works fine on some of the dealer's machine. but two of our dealers are facing this problem. these dealers are very big banks inside UK. When we tried our dealer's login on our machines everything worked fine. this is just happening to two specific dealers. what could be the reason for this? and how to avoid this? i have searched alot on internet but nothing worked for me. kindly give a solid reason and explanation. problem occurs only at IE.

when they click on a specific button , they see this exception. on that button we just open an aspx page in iframe. details of the error are given below.

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; InfoPath.2; .NET4.0C; .NET4.0E) Timestamp: Thu, 17 Nov 2011 14:19:14 UTC

Message: 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 'uamFuX1R5cGU9amF2YV9zY3JpcHQmRmluamFuX0x'. Line: 5 Char: 62099 Code: 0 URI: http://xyz.com/ScriptResource.axd?d=_FIiVFNdF1PHkbuLKG5hopSmLy4o3JvRIyD6vVyYwvpDZR7-f336pr-a6hLEOPIccb7DRK78POXYTQfl9EZSx4SxizvUioc19B1P43shEyWowLvhIGL3AeK1wy_YyeW1GriC7BqWtcuIU_bsb1M41M4Otm81&t=ffffffffe783cd7f&sfgdata=+sfgRmluamFuX1R5cGU9amF2YV9zY3JpcHQmRmluamFuX0xhbmc9dGV4dC9qYXZhc2NyaXB0+a

Solution

I was looking around on the net and found a similar question asked on StackOverflow - ASP.NET Ajax Error: Sys.WebForms.PageRequestManagerParserErrorException

There seem to be a number of things that could be causing this error, and this article might be a good helper to point you in the right direction. The article lists things to avoid when you are getting this error:

Calls to Response.Write(): Place an or similar control on your page and set its Text property. The added benefit is that your pages will be valid HTML. When using Response.Write() you typically end up with pages that contain invalid markup.
Response filters: The fix might just be to not use the filter. They're not used very often anyway. If possible, filter things at the control level and not at the response level.
HttpModules: Same as response filters.
Server trace is enabled: Use some other form of tracing, such as writing to a log file, the Windows event log, or a custom mechanism.
Calls to Server.Transfer():