Both wallet.dat and darkcoin.conf didn't exist. I created the .conf with your settings, restarted the wallet but error occurred

To be honest I've never encountered that error personally.
UNLESS YOU HAVE DARK COINS IN YOUR WALLET ALREADY, OR INCOMING COIN!!!
Just delete the .darkcoin file and re-download the darkcoin wallet (in case the one you have is corrupted, then start over.
Start the wallet
close thewallet
add the conf file to the .darkcoin directory in AppData
restart the wallet
Hope that helped
Do it but just save copy of wallet.dat if you have any DRK in your wallet.