Never saw this error before but if you want solomining you can try at xpoolx solomining pool. Mining.xpoolx.com:9999
-u YOURWALLETADDRESS -p x
You can solomine there as a temporaly solution. Fee is only 1.25 per block
Thank you very much for the quick reply and offering a quick solution.
Riecoin is worthless now; I don't mine for a profit. I just want to experience how original CPU mining works. That's why I do solo mining locally. I wish to understand what is happening here.