Windows 2003 Domain Permissions Not working

Ok I have setup a domain call test. With in the domain I have setup basic users and also specific groups that I add users to for example accounting group. I have folders of excel files with accounting info so I setup permissions to each folder adding only the accounting group to it. I gave them full control and went to advance for inherent for child directory’s and files. However when a user opens a file and attempts to change it and save it the error says its read only and they don’t have permission to save. however the file isn’t a read only attribute and neither is the directory. So just to figure this stupid thing out I gave the users admin rights to the whole domain and still they cant save a stupid excel file. Am I crazy? I have done this more than once and I feel like a noob. Any help would be great thanks.