Cepstrum analysis in condition monitoring of structures

Hi, everyone.

I am using cepstrum analysis, for output only vibration analysis of structures for damage detection. I have time domain vibration data in form of a (4096x2) matrix. The problem is when i apply cceps command, the following error comes.

Error in cceps>rcunwrap (line 147)

y(:) = y(:)' - pi*nd*(0:(n-1))/nh;

Error in cceps (line 80)

[ah,nd] = rcunwrap(angle(h));

Please help me out in eliminating this error/ send helpful material that how to use cepstral analysis on vibration data by using MATLAB.