Unable to access one machine on 4 machine home network

Home network consists of 2 desktops and 1 laptop with XP Home having
wired connections to router, and 1 laptop with XP Pro wireless. Until
recently all four machines were able to access all shared folders on any
other, now one (wired) desktop machine can see and open all the shared
folders on the other three and it's folders can be seen but not be
opened by them. When I try to open the first machine's shared folders
from any other I get the response;
**************
"\\machine name\folder name is not accessible. You might not have
permission to use this network resource. Contact the administrator of
the server to find out if you have access permissions.

Not enough server storage is available to process this command".
**************

The other three machines have full access to each other. There appear
to be no other problems and to the best of my knowledge I haven't made
any changes to the network since it was first set up.

Any suggestions?