Completely lost the ability to calibrate voltage

[JEJ]

I don't know what has happened but now I cannot calibrate REW for voltage. I use a signal generator and click the calibrate button but when I type in the voltage and click calibrate, the Full Scale Sine vRMS box reads some screwy number like 55 volts and the actual output is only a fraction of what I set it to be. I have used REW for years, but now I have to dump it for another software. REW calibration is horrifying.