Windows 7 Asks For Password On Accessing XP Computer?

Well there are 2 PC in my LAN:NBNotebook WiFi connection to my router NETGEAR DGN2200v3 Windows 7 Professional x64 SP1 DSKDesktop Cabled connection to my router NETGEAR DGN2200V3 Windows XP Home Edition 32bit SP3 If from DSK I try to access NB shared folders through network, everything is fine.If from NB I try to access DSK shared folders through network, the following window appears:The strange thing is that this problem seems to occur randomly! Sometimes it occurs, sometimes not (during the same session of usage of NB). This is annoying because usually I need to work with NB on files which are stored in DSK through local network, so if I need to apply a change to a file, sometimes I won't have a chance to do that.

Some minutes ago I configured DSK and NB so that the account for both has the same username and password.When on NB I try to access DSK shared folders, the window I posted above appears, I fill the data but neither this time I have granted access...This is what happens:- I reset NB WiFi connection- Using NB I try to access DSK shared folders --> everything is ok- About 5 minutes passes- Using NB I try to access DSK shared folders --> the authentication window appears, I fill the username and password fields but they won't be recognized