A problem with connecting to Oracle Server via .NET application...

If you can connect to Oracle Server from Toad or Oracle Enterprise Manager but can not connect via .NET application, probably visual studio is using a different tnsnames.ora file and this file is not up to date. To find this file and change its content follow the steps below:

1. Click Right on "My Computer" icon and select "Properties" option,
2. Click "Advanced" menu item and push the "Environment Variables" button,
   
3. Click on "PATH" item and push the "Edit" button,
4. Look at the content of the "variale value",
   
5. You should look for the paths like "....Client_1\NETWORK\ADMIN " entries in this stream. These paths includes tnsnames.ora files. Examine these files and update them.
6. Close "my computer" window.
7. Try to connect again.

Good Luck!!