Most of these errors occur when the terminal cannot read the files on the fileserver.
Ensure that the Bootdrv share on the file server enables full access to the user with which the terminal is logged in.
If you are using Windows XP Servie Pack 2, then you might have to disable Simple File Sharing in order to allow the terminal full access to the file server. To disable Simple File Sharing, open My Computer and select Tools/Folder Options/View. Disable 'Use Simple File Sharing' and click OK.
Follow the link above FAQ's check out the specifics on terminal and server setup.
Cheers,
Coorsman