Error Saving in Oracle Database

Hello there,
I installed oracle in my laptop running on windows vista ultimate. Honestly, I am new in using Oracle Database and I really want to learn more about it. At first I never had a problem using this software, until an error dialog box pops up on my screen when trying to save my file.
Error saving
“C:oracleproduct10.2.0db_1networkADMINtnsnames.ora”!
Probably the file is locked by another application.
How can I save my file without seeing this error message? What could be the cause of this problem? I closed other application running on my laptop when I save that file but this error is still visible. Anyone has an idea to resolve this issue? Thanks in advance to those who will post solutions!
