DTIPrep is based on your settings in the QC protocol. By default, image info and gradient info checks are set as "not failing overall QC" when these steps individually fail. You can interpret this behavior as a warning. In this specific case, the warning is that the image information is different from the one specified in the QC protocol, in particular the origin is different. This is actually expected, i.e. different scans should be expected to have different image origins, and thus you can safely disregard this warning. If the warning would be for differences in image size then you may be more worried (if you would assume that the images in your study should all have the same size). 

In any case, you can easily disable this QC step in the QC protocol  and thus you would not see this warning anymore.

Martin