Eureka!!!! I finally found the cause of the arc errors
On the first positional move in any of my programs, my CAM software (BOBCAD) was not outputting the X or Y axis position if it was zero. For example, if the first move was to X1.0 and Y0.0, it only output the X1.0, but there was no Y axis output in the gcode. When the next positioning command was a G02 or G03, MACH3 would attempt to interpolate the arc motion based on the current position of the axes in the workpiece coordinate system. Since the initial motion command did not always specify both the X and Y position, the value that MACH3 would use for the unspecified axis was whatever the current position happened to be. Normally, I position the machine to the location where I wanted to cut my inlay pocket, zero the axes and then load the program. When I did this, things worked fine. However, if I tried to load the program before I zeroed the axes, the unspecified axis position was always wrong (not zero). So, the arc error would be signalled. I think I just confused the issue by trying to load the program at different times. Sometimes I had zeroed the axes and sometimes I hadn't. In doing that, I never saw any consistancy in when the error would be flagged.
So, I've edited all my existing programs to set the missing X or Y axis output in my first move. In addition, I've changed the CAM configuration to force the positional output of both axes on initial moves. Under Setup->Coordinate format->Initial position, I changed the X and Y "Initial position" values from 0 to 9999.
