I am trying to mine VTC on Yiimp with vesion 2.0 x64, but after a while I get only errors. What am I doing wrong, please?

thank you

[2017-05-18 20:30:07] GPU #3: result for a4e30b61 does not validate on CPU!
[2017-05-18 20:30:07] GPU #4: an illegal memory access was encountered
[2017-05-18 20:30:07] GPU #3: result for a4e30b61 does not validate on CPU!
[2017-05-18 20:30:07] GPU #3: result for a4e30b61 does not validate on CPU!