If you get the error “The connection has failed” when you try to Import Metadata into the RPD, this post may help you to resolve it.

The solution is to: Create an Environment Variable called TNS_ADMIN and set its value to the directory of your tnsnames.ora file.
The TNS_ADMIN variable tells Oracle Client where to find the tnsnames.ora file which contains your data source details.

In case you need the details:
Click the Windows Start menu –> Right-Click on Computer –> select Properties
Then click on “Advanced system settings” on the left.

Click the “Environment Variables” button.
Then in the Environment Variables window, click New.
Enter the details for the TNS_ADMIN variable.  The value needs to be the path to your tnsnames.ora file, typically located at [ORACLE_HOME]networkadmin. The path will look something like the value shown below (it depends on where Oracle is installed on your system).

 Hope this helps.