A: In the PCA calculation the default is to use multivariate data.  This means that there must be a valid entry for every variable used in the PCA calculation.  This error message indicates that there are no samples that contain a valid entry for all of variables used in the calculation.  To check whether the samples you wish to use are multivariate or not use the “Apply Attributes to all Rows (Selected Data Not Null)” option under the Validate menu.  You must select an attribute colour first in the Attribute Manager which will then be applied to all of the data points that contain a valid data entry for all the variables selected in the Select Variables dialog.  For more information view the “Identify Multivariate Samples” training video which will enable you see which samples are multivariate for the selected elements and which ones are not.