Ignore the error and carefully trace your permissions. Start with object permissions on the gallery, then look for category permissions, if you're not using either of those and thus global only, then check the appropriate user group permissions.
Does that user group have these permissions:
Also make sure that the specific user group can actually see the gallery, having the batch permission will do them no good if that user group doesn't have:
tiki_p_view_file_gallery and possibly