If you load a G Code file and you see the error message "Radius to end of arc differs from radius to start", you will need to adjust your settings. Open Mach3 and go to Config>General Config and change the IJ mode to Absolute. Reload the file and it should load without that error message. Alternatively, you can add a G91.1 to the safe start up block of the G Code file. This will change the setting in that particular G Code file to use Absolute IJ Mode but will leave your default setting in Mach3 as is.