Hi Doug I posted this on the PixInsight forum but had no response. I just wanted to check it wouldn't be caused by a camera problem. The images look fine, and the ACP log I had checked with Bob who said it was fine. Unsure what is happening here. Will try and check it with MaxIm today Peter I am using the BPP script. On the last two objects I have imaged using LRGB, I am having an issue with Image Calibration for the Red channel. It will work fine only if I take out the flat frames, so there seems to be an issue with them only. But when I compare the images, and the FITS headers for the Red flats, and to the LGB flats, there appears to be no difference. I had obtained the flats using ACP Sky Flats and hadn't previously had an issue, but am now. I get the same error message : Applying bias correction: master dark frame... Dark frame optimization thresholds: Td0= 0.00030316 (162416 px= 0.968%) Computing master flat scaling factors... Error: Zero or insignificant scaling factor for flat frame channel# 0. (empty master flat frame image?) <*failed*> It will produce this whether I have a master flat, or the individual flat frames. In the FITS header for red, which is the same for the LGB there is : BITPIX 16 BSCALE 1.0000000000000 ( or so) BZERO 32768.000000000 I am using a master bias and master dark which work fine on the other channels. Unsure what is going on. Have tried it through Image Calibration instead but produces the same result. Any suggestions? Thank you.