Strange Standalone Web App Error

I have created a standalone web app that runs in on several virtual servers with Windows 2008 R2 and MS SQL 2008 R2 and connects to a SQL database via ODBC.
I have about 15 environments running this web app. I have also multiple instances of the web app running in the same server.

I have added an UnhandledException to the App to catch all the errors that are not managed in the program.
In the UnhandledException subroutine i write a file with error details and the stack trace.
This help me a lot to track almost every error, but occasionally i get this strange error that i can’t explain.
The error happens on almost every server with no exception. It happens once or twice a day.

[code]
Date: 2014-11-19 15:56:33
Error OutOfBoundsException occured.

Call Stack:
MemoryBlock.=StringValue%%oi4i4s
_WebMemoryBuffer.Write%%o<_WebMemoryBuffer>s
HTTPServer.HTTPRequestSocket.Event_DataAvailable%%o<HTTPServer.HTTPRequestSocket>
SSLSocket.Event_DataAvailable%%o
ConsoleApplication.DoEvents%%oi4
WebApplication.Event_Run%i4%oA1s
Delegate.Invoke%%
ConsoleApplication._CallFunctionWithExceptionHandling%%op
_Main
% main[/code]

Does somebody have already seen this error ?

Thank you in advance.

Marco

Do you know what browser is causing this error?

It seems that the error occurs before the app can detect the client browser when the client try to open the app.
The error is catched by the App.UnhandledException and not in Session.UnhandledException, and i can’t access session information.
However, today i track the errors that occurs and i try to find informations in the application log to find information to send to you.