We have 3 Oracle Servers. I used to be able to perform loopback like sqlplus@SID user/password or exp@SID user/pasword. Suddenly I it does not work. On UNIX Server I get: ksh: sqlplus@VDR1: not found
On NT I get: The name specified is not recongnized as an internal or external command,
operatable programm ot batch file

Nothing was changed on Oracle Servers.

Could anybody suggest something?