I think my flats were derived from APT maybe and lights from SGP, does this matter? Im not even sure. But this is the message I get. Does the nomenclature matter to Pixinsight as far as the name format of the files? I also tried clicking the "use master flat" check box and putting in a master flat stcked by DSS and it gives me the same error message. If I click run it will calibrate with darks but not flats. I also use flat darks and that box is checked.