If this has happened to you recently and you're running Windows 2003 SP 2, you need to check out the following links:
Microsoft Support about SP2 and TCP Chimney
KB Alertz about 2003 SP2 and TCP Chimney
Basically the same article, slightly different info in each. Apparently this is a MAJOR deal.
EDIT: The SQL Error message isn't the exact same, but it's something to check, anyway.