Error message in Console related to EWSExchangeWebServices

Question

My Mail seems to be using a lot of memory and I've noticed the following error message recurring. Can anyone help me sort out what it means and what I might do to fix it?
Thanks
26/01/11 9:13:41 AM Mail[336] * Assertion failure in -[EWSConnection sendMessage:forRequest:], /SourceCache/Message/Message-1082/MessageStores.subproj/EWSConnection.m:374
Received an unexpected error: Error Domain=EWSExchangeWebServicesErrorDomain Code=277 UserInfo=0x118348630 "The operation couldn’t be completed. (EWSExchangeWebServicesErrorDomain error 277.)", response: (null)
0 Message 0x00007fff86cfd6e4 -[MFAssertionHandler _handleFailureWithPreamble:description:arguments:] + 137
1 Message 0x00007fff86cfd649 -[MFAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 220
2 Message 0x00007fff86c3f01b -[EWSConnection sendMessage:forRequest:] + 1117
3 Message 0x00007fff86c4a5b9 -[EWSGateway sendMessage:forRequest:] + 79
4 Message 0x00007fff86c5da63 -[EWSRequestOperation executeOperation] + 104
5 Message 0x00007fff86d0bab9 -[MonitoredOperation main] + 229
6 Foundation 0x00007fff86768de4 -[__NSOperationInternal start] + 681
7 Foundation 0x00007fff86847beb __doStart2 + 97
8 libSystem.B.dylib 0x00007fff885a42c4 dispatch_call_block_andrelease + 15
9 libSystem.B.dylib 0x00007fff88582831 dispatch_workerthread2 + 239
10 libSystem.B.dylib 0x00007fff88582168 pthreadwqthread + 353
11 libSystem.B.dylib 0x00007fff88582005 start_wqthread + 13

Answer 1

Just guessing here, but look at this page,
http://msdn.microsoft.com/en-us/library/dd877045%28v=exchg.140%29.aspx
Does anything there "ring any bells" on anything you might have been doing recently? Of course I don't think any of that would have any relationship with the apple Mail app.