Cannot keep Guest in Access this computer from network

[Guest]

I have two PCs with WinXP Pro connected by LAN via a switch. Although PC A
can have access to PC B, PC B cannot see always PC A. I enabled Guest account
and added it in the User Right 'Access this computer from Network' and the
problem was solved. There was also no value in User Right 'Deny access to
this computer from network'. But after a while the field lost its containt (
Guest was dissapeared from User Right 'Access this computer from Network')
and PC A became unaccessible. I added it again and after a while it was lost
again. Does anyone know how can this happen and how can i resolve it?

 

[Guest]

Do you have a Firewall activated on PC-A? If there is check the settings,
also how are you accessing each PC with remote desktop or another software?

Hope this helps...

 

[Guest]

there is no firewall on PC-A. I have installed the LAN with "Setup a home or
small network". The problem still persists. Any other idea?
Thanks anyway