OperationContract method '{0}' in type '{1}' does not properly implement the async pattern, as more than one corresponding ...

OperationContract method '{0}' in type '{1}' does not properly implement the async pattern, as more than one corresponding method '{2}' was found. When using the async pattern, exactly one end method must be provided. Either remove or rename one or more of the '{2}' methods such that there is just one, or set the AsyncPattern property on method '{0}' to false.