Unexpected nested arrays after using lookup

Hi! I am using the lookup function in MathCAD 14.0. Specifically I have a file containing the results of a FFT performed by the oscilloscope I have connected to an amplifier I am testing and wish to extract and compare the harmonics generated as the amplifier is overloaded.

I can read the file and plot the FFT. I know the frequencies at which I wish to record the signal levels and create an array Fpk with those frequencies in it. This is then used with the two single column arrays (frequency and amplitude(dBm)) into a lookup equation to generate the variable Peaks. I expect Peaks to be another single column array but the lookup returns an array of 1x1 arrays.

What am I missing? Am I do something incorrectly? How do I convert from the array of 1x1 arrays to a single column array?

Any help will be gratefully accepted.

Martin