I had the same problem once with my WCF Service. The problem occurs when I used unknown types to transfer between the service and the client.
try the microsoft test client to connect to your service and maybe this tool will give you some clue to which method is wrong. more info: see
http://msdn.microsoft.com/en-us/library/bb552364.aspx[
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Otherwise you can also comment all the Operationcontracts one by one and try to update your service reference each time. So you can discover which is the incorrect OperationContract