"The server instance specified was not found. Please specify the server's address and port." Error

Yesterday I ran into this problem. I tried to deploy Web Parts package with stsadm.exe and then bam!!

“The server instance specified was not found. Please specify the server's address and port.”

On Saturday everything worked like a charm, and on Sunday that error (don’t ask how I know it worked on Saturday and Sunday ;-) ).
I didn’t do anything unusual. I’ve checked the Windows Auto update log, and it installed many updates on Saturday morning. I thought that it was it.

Anyway, what helped me is this post on Mohammed Jeelani's Blog.

For me it was the first reason.