Migration to Office 365 Failed - CommunicationErrorTransientException at 95%

Hello

I am working with a client to the point where they can move their mailboxes to Office 365 themselves.   I am having some issues - the synch works fine but when it comes to finalising i keep getting this error over and over again

FailureType       : CommunicationErrorTransientException

FailureHash       : 19cc

FailureCode       : -2146233088

MapiLowLevelError : 0

FailureSide       : Source

FailureSideInt    : 1

ExceptionTypes    : {Exchange, Transient}

ExceptionTypesInt : {1, 2}

Message           : The call to 'https://smtp.mmca.co.nz/EWS/mrsproxy.svc mmexchange.mmca.local (14.3.227.0

                    caps:05FFFF)' failed. Error details: The remote endpoint no longer recognizes this sequence. This

                    is most likely due to an abort on the remote endpoint. The value of wsrm:Identifier is not a known

                    Sequence identifier. The reliable session was faulted.. --> The remote endpoint no longer

                    recognizes this sequence. This is most likely due to an abort on the remote endpoint. The value of

                    wsrm:Identifier is not a known Sequence identifier. The reliable session was faulted.

My set up is 1 Exchange 2010 server.