Hello, I am trying to use the aCGH packaged to do HMM smoothing of copy number data. However, for certain samples, I get an error message when trying to compute the standard deviation. "Warning: MAD could not be computed for one of the samples" Does anyone know what is causing this problem. My input data is 'unsmoothed' copy number estimates taken from Affymetrix's copy number tool. This problem does not occur for every sample. Any insight into this matter would be helpful. Thanks, Neil