Why do I receive system error 51 when I use a 16-character Fully Qualified Domain Name (FQDN) to connect to a remote machine?

A. When the FQDN is exactly 16 characters long, both Windows XP (pre-Service Pack 1--SP1) and Windows 2000 (pre-SP3) generate an error when creating a share to a remote machine that's running Windows Me, Windows NT 4.0, or Windows 9x. This error is the result of NetBIOS over TCP/IP (NetBT) incorrectly identifying the FQDN as a NetBIOS name. Subsequently, when NetBT can't find the name, you receive the error "System error 51 has occurred. The remote computer was not available." For example, the following connection might result in the error:

net use * \\host1.domain.com

To resolve this error, apply XP SP1 or Win2K SP3 or contact Microsoft for a hotfix--for XP, you need netbt.sys 5.1.2600.16 or later, and for Win2K, you need netbt.sys 5.0.2195.3769 or later.