Common Issues Connection Refused: Ensure the server is running before starting the client. Invalid Message Format: Messages must follow the format message:checksum. Checksum Mismatch: Indicates ...

That took care of my SQL Express issue, I was able to do a network search and find the server in Management Studio by enabling TCP, adding port 1433 to all IP's, and opening the ports in the ...

My guess is that the authentication of the client is being done via a TCP/IP connection, and the SQL server cannot find your client machine, because you don't have TCP/IP bound to CFMN.