newrb training sudden MSE drop

Hi there. I have a trouble regarding newrb function training involving 78 training data points. When I started training the function, the MSE dropped steadily as more neurons were added. On the 76th epoch the MSE was huge, however, on the next epoch at 77 it dropped significantly to 3x10^-20 as shown below

NEWRB, neurons = 75, MSE = 70892.4 NEWRB, neurons = 76, MSE = 1224.41 NEWRB, neurons = 77, MSE = 3.7122e-20

Is this correct? Sometimes I also noticed at other spread value the 76th epoch MSE was NaN and then at 77th epoch the MSE plunged to 1x10-22. Is this also correct ???