When cutting a circle I get a error code 50. Cutter doesn't come all the way around to the start point. Why not? Is this table travel error. How do I cure this?

It's saying you have made a syntax error within your G code. Your end point
is incorrect or one of your arc centers or radius call are incorrect.
The Centurion 4 is very specific about its radius/circular milling.
The correct syntax is G2 0r G3 R# I# J# X# Y#
where
G2 or G3 is arc direction clockwise or counterclockwise
R=radius size
I=absolute coordinate of X axis arc center
J=absolute coordinate of Y axis arc center
X= arc end point in X axis
Y= arc end point in Y axis

The program was:
G2 R1.025 I-3.6875 J0 X-2.6625 Y0

Your arc sequence looks correct. You must have a G1 and feedrate somewhere before the arc. Here is small program with a .500 endmill,
boring a .716 diameter hole x .250 deep.

G90 G40 G80 G100 G17
GO X-.5 Y-1.437
S2700 M3 M8
G101 G300 Z.1
G99
F10. G1 Z-.250
F8. G1 Y-1.329
G3 R.108 I-.500 J-1.437 X-.500 Y-1.329
G1 Y-1.437
G99
M5
G100
G98
M2