ORA-12154: TNS:could not resolve the connect identifier specified
This is one of the most common Oracle errors and it is basically telling you that you are trying to connect to a database name that is unknown to the system.
The most common cause are typos in your connection string or network configuration files. So be sure to check your tnsnames.ora and listener.ora files. Also make sure your ORACLE_HOME and ORACLE_SID are set to the proper environment. Sometimes you also need to make sure your TNS_ADMIN paramter is set if you’re using an alternate location for those configuration files. Everyone makes mistakes and even someone that works in these environments every day can miss a small detail on occasion. Having a second set of eyes take a look ususally can help you spot the error.