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Dear All, when conducting a second level VBM8 longitudinal data analysis on difference images (T2-T1) produced with ImCalc I experience a problem which I cannot solve. After conducting the preprocessing as described by the VBM8 toolbox manual, I want to do some correlations bet the structural difference between the two time points and clinical variables. But when I conducted a correlation analysis I received the following error: Spatial non-sphericity (over scans) : .. writing resels/voxel image Failed 'Model estimation' NaN's cannot be converted to logicals So, could anybody tell what's wrong? I appreciate any kind of help! Thanks, Martina