The system has X cores, but Corona is configured to use only Y - rendering will not run at optimal speed.
This message will occur whenever you removed more than two rendering threads from rendering using the # of threads option. It serves as a warning in case the setting was accidentally set to a wrong value.
- Make sure you do not remove more threads from rendering than you really need to.
- In case you desire to keep your setting, you can dismiss this error by clicking "Ignore similar messages” button in Error Messages window.