I receive back a good oauth_verifier value from the server, but it is not being passed on via the ProcessUserAuthorization call to the access_token endpoint.

I'm using DotNetOpenAuth 3.3.1, and the WebConsumer implementation. The server I'm working with is using OAuth 1.0a not 1.0.1.

Do I need to force DotNetOpenAuth to use 1.0a?

2010-01-16 13:19:44,343 [5] DEBUG DotNetOpenAuth.Messaging.Channel [(null)] <(null)> - After binding element processing, the received UserAuthorizationResponse (1.0.1) message is: 
    oauth_verifier: dEz9lE9AA1gcdr6oCbmD
    oauth_token: vauHNVOCITlbGCuqycWn

2010-01-16 13:19:44,346 [5] DEBUG DotNetOpenAuth.Messaging.Channel [(null)] <(null)> - Preparing to send AuthorizedTokenRequest (1.0) message.
2010-01-16 13:19:44,346 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Binding element DotNetOpenAuth.OAuth.ChannelElements.OAuthHttpMethodBindingElement applied to message.
2010-01-16 13:19:44,346 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Binding element DotNetOpenAuth.Messaging.Bindings.StandardReplayProtectionBindingElement applied to message.
2010-01-16 13:19:44,346 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Binding element DotNetOpenAuth.Messaging.Bindings.StandardExpirationBindingElement applied to message.
2010-01-16 13:19:44,346 [5] DEBUG DotNetOpenAuth.Messaging.Channel [(null)] <(null)> - Applying secrets to message to prepare for signing or signature verification.
2010-01-16 13:19:44,348 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Signing AuthorizedTokenRequest message using HMAC-SHA1.
2010-01-16 13:19:44,349 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Constructed signature base string: GET&http%3A%2F%2Fx-staging.indivo.org%3A8000%2Foauth%2Faccess_token&oauth_consumer_key%3Doak%26oauth_nonce%3DgPersiZV%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1263676784%26oauth_token%3DvauHNVOCITlbGCuqycWn%26oauth_version%3D1.0
2010-01-16 13:19:44,349 [5] DEBUG DotNetOpenAuth.Messaging.Bindings [(null)] <(null)> - Binding element DotNetOpenAuth.OAuth.ChannelElements.SigningBindingElementChain applied to message.
2010-01-16 13:19:44,351 [5] INFO  DotNetOpenAuth.Messaging.Channel [(null)] <(null)> - Prepared outgoing AuthorizedTokenRequest (1.0) message for http://x-staging.indivo.org:8000/oauth/access_token: 
    oauth_token: vauHNVOCITlbGCuqycWn
    oauth_consumer_key: XXXXXXmyComsumerKeyXXXXXX
    oauth_nonce: gPersiZV
    oauth_signature_method: HMAC-SHA1
    oauth_signature: xNynvr2oFlqtdoOKOl2ETiiTLGY=
    oauth_version: 1.0
    oauth_timestamp: 1263676784

2010-01-16 13:19:44,351 [5] DEBUG DotNetOpenAuth.Messaging.Channel [(null)] <(null)> - Sending AuthorizedTokenRequest request.
2010-01-16 13:19:44,351 [5] DEBUG DotNetOpenAuth.Http [(null)] <(null)> - HTTP GET http://x-staging.indivo.org:8000/oauth/access_token
2010-01-16 13:20:34,657 [5] ERROR DotNetOpenAuth.Http [(null)] <(null)> - WebException from http://x-staging.indivo.org:8000/oauth/access_token: 
<h4>Internal Server Error</h4>

A pastebin link to the log4net log