I,m not all that sure about key loading with that box, but there all about the same,
Go to key file loading page, select the correct encryption, enter the provider key FF FF FF enter the index key OC, enter the 8 byte plain key.
FF FF FF FF FF FF FF FF now at the bottem of the page there should be a "Store " key or click OK to store. Miss this and all the keys you have entered will be lost.
Return to your main menu and sellect the channel you want, It might play streight away, you might have to wait a few minutes for it to update the key. BUT if you have entered everything correctly it should work