Execute a SQLPlus command in a ksh script

I have developped a SAP CPS  KSH script to be executed in a job chain. This script includes a command line like : sqlplus -s <user>/<password> \@<sql_file_to_be_execute>

When I execute the script I have the error :

ERROR: ORA-01017: invalid username/password; logon denied

But when I logon the server with the user I used to execute the job in SAP CPS and execute exactly the same command line as below I have no error !

What's the matter ? (The user is declared in SAP CPS security, Identification information.

Please help. Thanks.