Ohhh. I wish elsewhere right now so that I could test this, but it looks like the maximum number of named pipes are automatically determined by the operating system based on the resources available. When the error occurs, take a look at "Computer Management", and I think it's sessions to see the pipes currently in use. (I don't think that is IPC$ traffic, but I could be wrong. I'll have to get back to my system tomorrow to check...)
(Anyone else want to jump on that one before tomorrow for an assist?)
In any event, I suspect if the system is working correctly for weeks at a time, without problems, and they SQL Server isn't patched, that you are getting infected every few weeks by the Slammer virus. You can look here:
http://isc.sans.org
at the volume of port 1434 traffic to see that Slammer and it's ilk are still alive and well on the net. :-( )