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the red errors you are getting while mining are okay as long as the miner doesnt crash, you should check your steem power it must be increasing with time

The issue was resolved! I closed steem and run it again and it started mining! Thank you, r3b37!

Alright, thank you for your assistance, once again!
So should I just wait a few more hours? Also, since steem power increases anyways, how will I know if the miner is working?

have you downloaded the updated miner from https://github.com/btscube/steem/releases/ ?

Latest is "steem-win-x64-012.zip" and a updated blockchain from http://www.steemitup.eu/ for the new miner with config.ini modified as per your account and settings.

Yes, I did it last night, so it should be up to date.
The syncing process is over! But unfortunatelly I'm not mining, because I got this error:

Could you please help me solve this?