Intermittent Failure

I have a strange problem. I have a small network with two Win XP
computers, one a wireless laptop and one a wired desktop and a cable
modem attached to a router. Most of the time everything works
perfectly. But sometimes when I try to access the desktop computer, I
get an error message about no permission and path not found. If I go
to the desktop and access the laptop, everything is OK. And a few
minutes later, the laptop can again access the desktop. The laptop
never loses the internet connection.

Somehow, on an intermittent basis, the laptop loses access to the
desktop computer but maintains it's internet connection.

Anyone have any thoughts?

Regards, hawk.