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I have googled myself silly (and my customer is getting really fed up). I am getting frequent but inconsistent 400 Bad Request errors on my Silverlight app, about 300 to 700 errors a day from about 10 users so the frustration is understandable.

I have gotten the FREB logs but honestly I don't know what to look for as I don't see anything specifically wrong, what should I be looking for? I realise that this question could have many answers and that I'm not being specific, but I can't even imagine what specifics to include...

Here's some detail:

  • Silverlight 5 with WCF services (not RIA services)
  • Win Srv 2008 R2 with all updates (IIS7)
  • All traffic is on the LAN, and they have checked for retransmissions
  • ASP Net 4.0
  • The server is not out of RAM etc, and does not have that many users accessing it
  • SSRS 2008 R2 is also running on the server, but does not seem to have an impact on this

I'll be happy to email 1 or 2 log files if someone is prepared to look at them...

Adriaan Davel
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    Start to check which module returns 400 and see if there is a status code for you to further analyze. When in doubt, open a support case via http://support.microsoft.com – Lex Li Jan 14 '14 at 14:38
  • Thanks Lex Li, its the IsapiModule (I'm pretty sure) what do I do next? – Adriaan Davel Jan 15 '14 at 19:56
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    If you are using classic pipeline then I think IsapiModule might be a proper place to return such information. To move on, try to enable WCF tracing and locate the cause of 400 from there, http://msdn.microsoft.com/en-us/library/ms730342(v=vs.110).aspx. Note that a WCF function might return 400 itself, as this is the freedom WCF grants (read http://blogs.msdn.com/b/endpoint/archive/2010/01/21/error-handling-in-wcf-webhttp-services-with-webfaultexception.aspx for an example). – Lex Li Jan 16 '14 at 00:40
  • Ok, used WCF tracing, essentially I get a "There is a problem with the XML that was received from the network" exception with inner exception "The body of the message cannot be read because it is empty". I can't understand how Silverlight can generate this type of problem inconsistently... Or am I looking in the wrong place? – Adriaan Davel Jan 16 '14 at 08:05
  • From the tracing we can only check the server side data. If you can see from the trace that the XML message body is indeed empty, you might guess what has happened on the client side. I would suggest capturing traffic from client side as well as server side to better understand the case, but such capturing might be technically impossible if it is so random. – Lex Li Jan 16 '14 at 08:11

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