prefect

hi! i am having some issues with file transfer from our server 2008 to our windows 7 clients. i am currently trying to copy fairly large files over the network, but i get an error saying there is some kind of signature problem (error 0x80090006 Invalid signature) , but i can't for the life of me find the solution. i only have problems while copying from the server to the clients, not the other way around. i am using a clean installation of server 2008, and now there is only AD, DNS and the file services installed. i had this problem earlier, and i tried a reinstall, but i still have the same problems now. this server is going to act as a file server only, so getting this issue solved is vital for us. any thoughts? thanks