I cant acces shares on another pc

I have 2 pc, xp pro machine and server 2003 both are on the network connected via cat 5 and are on the same range of IP. I have shared folder on the server where the xp machine is supposed to access the server in order to install a client software located in that server’s shared folder. The thing is I can browse/access the server but when i open the shared folder i get a message “Folder name is not accessible.You do not have permission to use this network resource. Please contact the administrator……bla bla bla”. What colud be the problem. please help!