SQL Server Network Interfaces: Connection string is not valid [87]

Question

When I am running this from cmd on my SQL Server 2008 instance:

sqlcmd -U sa -S mymachinen_name\\MSSQLSERVER

(where MSSQLSERVER

Answer 1

Typically, the MSSQLSERVER service is the service of a un-named default instance.

Therefore, try this:

sqlcmd -U sa -S mymachine_name

(without specifying any instance name - just the machine name)