Access Denied Win 2000 server-scheduling

Main server is running Win 2000 Server. I have a folder shared on this server with full access rights to all users. I have a PC running NT Workstation. This PC dials a remote PC to pick up some files via FTP – these files are copied to the C drive of the NT workstation PC. The folder on the server that I have shared is mapped as drive F on the NT Workstation PC. I have a batch file set up to copy the files from the C drive to the F drive. If I run this batch file it works perfectly. If Ischedule this batch file to run at a certain time using the AT command or Nortons scheduler I get access denied when the batch file tries to access the F drive.