Internal math error when using interpolation

I am using MATLAB to process and evaluate reflection coefficients of antennas.

The data is saved and used as an Mx2 array, where the M is the length of the x-axis data points, (or sample points). The first coloumn contains the values of the frequency points and the second coloumn contains the corresponding reflection coefficient values.

I use the 'interp1' function, which worked for the arrays of length 501, but the other array sized, 402, 404, 408 and 505, the following error occurs:

Error using matlab.internal.math.interp1

Sample points must be unique and sorted in ascending order.

Error in interp1 (line 188)

VqLite = matlab.internal.math.interp1(X,V,method,method,Xqcol);

I checked, and my sample points are unique and in ascending order, but the error still persists.

Here is a little snippet of the data

Sample point Reflection coefficient value

200 0.979472485068518

204.500000000000 0.977219575869647

209 0.974701356449019

213.500000000000 0.971883119143293

218 0.968724759813479

222.500000000000 0.965179866285502

227 0.961194345460292

231.500000000000 0.956704944454534

236 0.951637259422883

240.500000000000 0.945903325003744

245 0.939398658119580

Any and all help will be greatly appreciated.

[Stephan]

Please provide the data

[Pieter Grobler]

It appears that a sample point was duplicated when I first created the data.