Assign Software to Computer

I am trying to use group policy to assign Office XP to a group of computers. I have created software installation task in group policy, and have assigned it to the domain computers group. I have a DFS point, which includes read permissions for Domain Computers, that is my install point. When I try this on a computer, I get an error stating “installation source is not valid”. The path is correct, and the permissions are correct to my knowledge, but it just won’t install. I can create the same task, and assign it to a user and it works fine. Any ideas?
Bill