pagefile.sys error

After adding a client to my system (1 Server, 10 Clients) and trying to map a network drive on the client, the server tells me I can’t map that network drive. The system did let me map 1 drive on the server but not the second drive.
After going tothe server to check the permissions on the problem drive I noticed it did not show that particular user so I added the user to the permissions. Every time I tried to add that user and click OK I get and error:
“The following error occured applying security information to G:\pagefile.sys”.
“The process cannot access the file because it is being used by another process.”
Even after closing all resources to make sure nobody is logged on I still get the error
Any Help
Thanks