If I remove the flats and darks, this error message does not come. BIAS work alone.

This is with 1.077 right? And the exact same frames didn't cause an issue with 1.076 or 1.075?

Yes, that happened with the update to 1.077
I have now installed 1.075 again. Now I have the same error message here.
I'm testing other data, here is the same error message.

Obviously this error message comes from the Darks. Now I only used 30 of the 50 from the middle. And now it works 🙂

I uploaded the 50 darks here. Maybe this will help you find the mistake.

https://www.dropbox.com/s/hw2ckxgrzstyegw/300s.rar?dl=0

Ah great, yes it sometimes happens when calibration data has some issue. Might be worth for you to check the difference between the darks that didn't work and those that did, just to prevent it in the future. Thanks for uploading, can you pinpoint which frames caused the issue?

I looked through the darks one by one and saw no anomalies.

@daniel_n,

That error is indicative of a problem where you are calibrating data that incomaptible like monochrome data with Bayer CFA or 3-channel (RGB) Master frames or vice versa... check your data, if it's Bayer CFA data, have you enabled Force CFA in 0) RAW/FITS? Are all masters created as CFA masters?

Can you share frames of all types? Some lights, darks, flats, bias? I will make sure that it is solved.

Mabula

I am using the ASI 183 MC Pro. And I use these settings.

Today I tested it again with the exact same data. And now without an error message!
I don't know what yesterday was. I also installed APP on my laptop yesterday. And there I had the same error message.
But not anymore today 😀