Have you tried, if you can actually do SQL with that user? Maybe there is a problem with the SQL authorization?
Does the following work for you?
>sqlcli -d tz79 -u dba,dba select * from dual
| DUMMY |
| ----- |
| a
1 row selected (1318 usec)
dbmcli -d tz79 -u dba,dba sql_execute select * from dual
OK
END 'a'