I am running a few analyses with r.regression.multi in Grass 7. For a few rasters that I try to correlate, the following error comes up, however: "ERROR: Not enough valid cells available". I cannot see how the rasters I am trying to correlate in theses cases differ from the rasters where the analysis works. They match in dimension and location. Any ideas where the problem could lay?
Addition: Here a screen shot of another situation: the regression is only calculated for a certain area.