ORA-12154: TNS:could not resolve the connect identifier specified

I am getting this error: "ORA-12154 could not resolve the connect identifier specified" when I I am trying access Oracle database using OracleConnection in Visual Studio.

I had 11g clients installed, I found that the following two environment variables were missing in my computer, after I added them, I can access my Oracle database.

ORACLE_HOME = C:\Ora112

TNS_ADMIN = C:\Ora112\FClient\network\admin

Also, double check the follwing environment variable is there:

PATH = C:\Ora112\FClient\bin;....