To make sure that the server recognizes the user name, attempt to open a telnet session from the client, with that user name.
If you can perform the process from UNIX, you may have incorrect attach point configuration or client connection--but keep in mind that you cannot replicate all actions performed from a PC, on UNIX. Open a telnet session and try the process from UNIX. For example, if you have printing problems, telnet to the server and use the lpr command to send a file to the printer. If the action works under UNIX, check the client and server configurations.
Check this using another program. For example, to check the TCP/IP configuration, use ping from UNIX.