Oracle Developers guide 10g is not connecting to server
You said "I check my TNSNAMES.ORA file at my database host machine."  (emphasis mine).  The tnsnames.ora file is used by the client process. There are some other things to check as well. See this. But from what you've shown so far, I'd guess you are looking at the wrong file.  Oh, and since the nature of the problem means oracle couldn't even get as far as sending a request (because he didn't know where to send it), the listener never enters the picture for this error.