ASP.NET CryptographicException in application log

[Chris]

Dozens or hundreds of times a day we see events like the one below.
It is not for every instance of someone connecting to the server,
however. I cannot seem to tie it down to a particular browser or set
of browsers. I can replicate it on one or two PCs in our office, but
not all. IE6 fails to load our captcha page when users click the link
to get to it, but a reload brings it up. Other browsers will also
trigger the error on the web servers (there are two IIS6 servers on
Server 2003 behind a Cisco content management switch), without seeing
any ill effects in their own session.

Our CAPTCHA page was developed last December and we have not made any
changes to it since. I'm not the developer and while I know a little
bit of ASP.NET, I can't say I've yet achieved an understanding of the
functioning of the page producing this error. Does the recaptcha.dll
file get continually updated, and are we behind the times?

I think this error has probably been occurring ever since it was
deployed, but recently some users have been saying they've been
getting errors when trying to access the page and get past it. I
unfortunately didn't get a screenshot or details of the user's PC,
however. All I got was the error message translated from the user
through the help desk: "License error. The read operation failed. See
entered acception." I can't even be sure it was even in the browser
window. Could be something else entirely as I've never been able to
replicate that behavior, even when getting the error below.

Any suggestions on troubleshooting or resolving this would be
appreciated.


Event Type: Warning
Event Source: ASP.NET 2.0.50727.0
Event Category: Web Event
Event ID: 1309
Date: 11/19/2010
Time: 10:32:07 AM
User: N/A
Computer: mywebserver
Description:
Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 11/19/2010 10:32:07 AM
Event time (UTC): 11/19/2010 4:32:07 PM
Event ID: 6a95570f57844700a452cd2da68b7c1a
Event sequence: 578
Event occurrence: 19
Event detail code: 0

Application information:
Application domain: /LM/W3SVC/1/Root/AppName-1-129346466486061045
Trust level: Full
Application Virtual Path: /AppName
Application Path: E:\WebSites\public\AppName\
Machine name: mywebserver

Process information:
Process ID: 2540
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE

Exception information:
Exception type: CryptographicException
Exception message: Padding is invalid and cannot be removed.

Request information:
Request URL: http://www.oursite.edu/AppName/WebResource.axd?d=mBk20lcPOLZDi-
FIqkvWjg2&t=634129968592727281
Request path: /AppName/WebResource.axd
User host address: 10.70.100.63
User:
Is authenticated: False
Authentication Type:
Thread account name: NT AUTHORITY\NETWORK SERVICE

Thread information:
Thread ID: 5
Thread account name: NT AUTHORITY\NETWORK SERVICE
Is impersonating: False
Stack trace: at
System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[]
inputBuffer,
Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32
outputOffset, PaddingMode paddingMode,
Boolean fLast)
at
System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[]
inputBuffer, Int32
inputOffset, Int32 inputCount)
at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
at
System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean
fEncrypt, Byte[] buf, Byte
[] modifier, Int32 start, Int32 length, IVType ivType, Boolean
useValidationSymAlgo)
at System.Web.UI.Page.DecryptStringWithIV(String s, IVType ivType)
at
System.Web.Handlers.AssemblyResourceLoader.System.Web.IHttpHandler.ProcessRequest
(HttpContext context)
at
System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute
()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step,
Boolean& completedSynchronously)


Custom event details:

For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.

[Adrian Godong]

I don't think reCAPTCHA caused this. We're not using any encryption
and it comes from a request to an .axd.

This looks to me like some sort of problem in your configuration. It
is encrypted and the decryption failed. You may want to reencrypt your
configuration file and replace the one on the servers.

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Adrian Godong
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