Why is this message appearing?
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!
GPU #0 returned incorrect data!

too much OC!!
what does that mean? Does it interfere with mining in any way?
most likely you are running the GPU with too high temps and needs the processors to be resealed. Low voltage can do it too. Reset the GPU to the default values and see whats happens. If it continues under clock it. How old is the GPU? Also how many GPU's are on the motherboard and power supply do you have?
Is already in the default value but the error still persists.
I have 3 GPU and 3 more power supply one 600 power color shocker and 2 corsair cx 500.
Isolate everything by only having minimum components
so, only one keyboard & mouse; monitor, memory module, CPU, 1 GPU, your 600W power supply, motherboard, & SSD or HD
Also remove any risers from system
then turn and attempt to mine. turn off system
If it works than add another GPU with or without the riser and test again
If it works then add another GPU with or without the riser and test again, however if it failed then your issue is most likely power.
You'll need to get a dual power supply adapter and either use the 600W with the 500W power supply or use both 500W power supplies
using things like flash drives, USB 3.0/3.1, in place of HD or even SSD's, DDR3L/ DDR4 will help as well with saving power to the rest of the system.
Another thing to remember to is that you should only have the 500W power supplies only supplying about 320W that includes the 20% that is lost due to inefficiency if it's and 80+ white label power supply.