Data Entry Window Doesn't Open

If you cannot open a Data Entry Window and find the error ORA-12154: TNS:could not resolve the connect identifier specified in the opaServer.out file in a location like: middleware_home\user_projects\domains\OPADomain\servers\Server_Name\logs\Server_Name.out, it is probably because you have not added the database where the CRF is stored to the tnsnames.ora file on the application server.