Failed to serialize the message part - BizTalk

“  Failed to serialize the message part <RequestMessage> into the type <RequestMessageType> using namespace <Namespace>. Please ensure that the message part stream is created properly. “

if you are getting this error. . try validating your instance with the schema file. generate the instance and validate it or even with the custom input message . do a file receive and send and validate it. most probably the error is due to validation else check the namespace. or there are chances it could be the proxy class (.dll). generate the proxy class using wsdl.exe and the wsdl . create the orchestartion and use Basic Httpbinding in the send port. for receive port add the soap action.