I have got Oracle DB's version 18 and version 19 and they all work fine but the Nagios monitoring checks for v19 all give me:
CRITICAL - ORA-12154: TNS:could not resolve the connect identifier specified. I even have got on one server both versions but monitoring checks for v19 not working. They are all set the same way (tnsnames.ora, and .cfg in monitoring serv.) but I still missing something for v19 only.
Tried to find the same issue on the internet but I didn't. Also checked the connection and is DB work and is OK. Compared to the conf. files from v18 and v19 looks OK.
Be sure that you use correct credentials when it comes to user and password in -l and -a I also experienced this kind of errors in past, during creation of checks but proper USER solve it.