"The prelogin packet used to open the connection is structurally invalid; the connection has been closed. Please contact the vendor of the client library."

When Microsoft SQL Server is scanned by runZero, it may report an error:

The prelogin packet used to open the connection is structurally invalid; the connection has been closed. Please contact the vendor of the client library.

This is normal behavior for newer versions of SQL Server. The runZero Explorer doesn’t try to authenticate, but there’s no way to close the connection cleanly without authenticating and without triggering the error.

This means that the only way to prevent the error is to stop scanning the device with the SQL Server probe enabled. If you do that, you will no longer obtain any information about the SQL Server version found.