Connect to Oracle Dadabase by OracleConnection

I installed Oracle 10g XE in my box, and then Oracle Developer Tools for .Net (ODTwithODAC1020221). After the installation, I started to work on .Net C# project against Oracle DB.

The first thing I have to do is to build a connection. At the start, I got exception when I tried to open an OracleConnection to userID=HR, Data Source=XE:

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

Without connection, I cannot continue to do anything about the Oracle DB. After one day struggle, I finally found the reason from Oracle Developer Tools Forum: the home directory for Tools Kit is different from the Oracle db home directory! I have to follow the instruction to copy Oracle's TNSNAMES.ORA to the Tools' home directory. After that, the problem is solved!