Windows 7 Machine Cannot Access Win2003 Machine In A Workgroup?

i have Lan, all computers are windows 7 proffisional and one machine is windows 2003 , workgroup . i made shared folder in windows2003 , some computers can access the shared folder and others can not.when i open network , i see the 2003 computer, when i try to access it , it asked for user name and password. the user is administrator for all , when i enter the user and password from many computers in the lan it is work correctly but in one machine with the same settings its says , you have no permession to access this computer.