preprocessing execution failure

23:09:02: Welcome to siril v1.2.0-beta2
23:09:02: Supported file types: BMP images, PIC images (IRIS), PGM and PPM binary images, RAW images, FITS-CFA images, Films, SER sequences, TIFF images, JPG images, PNG images, HEIF images.
23:09:02: Setting CWD (Current Working Directory) to 'C:\Astro\M82'
23:09:02: Parallel processing enabled: using 12 logical processors.
23:09:04: Searching scripts in: "C:\Program Files\Siril\scripts"...
23:09:04: Loading script: Mono_Preprocessing
23:09:04: Loading script: OSC_Extract_Ha
23:09:04: Loading script: OSC_Extract_HaOIII
23:09:04: Loading script: OSC_Preprocessing
23:09:04: Loading script: OSC_Preprocessing_WithDrizzle
23:09:04: Loading script: RGB_Composition
23:09:04: Loading registration method: 1-2-3 Stars Registration (deep-sky)
23:09:04: Loading registration method: Global Star Alignment (deep-sky)
23:09:04: Loading registration method: Two-Pass Global Star Alignment (deep-sky)
23:09:04: Loading registration method: Image Pattern Alignment (planetary - full disk)
23:09:04: Loading registration method: KOMBAT (planetary surfaces or full disk)
23:09:04: Loading registration method: Comet/Asteroid Registration
23:09:04: Loading registration method: Apply Existing Registration
23:09:04: Default FITS extension is set to .fit
23:17:57: Setting CWD (Current Working Directory) to 'C:\Astro\M82'
23:18:13: Starting script C:\Program Files\Siril\scripts\Mono_Preprocessing.ssf
23:18:13: ############################################
23:18:13: #
23:18:13: # Script for Siril 1.2
23:18:13: # February 2023
23:18:13: # (C) Cyril Richard
23:18:13: # Mono_Preprocessing v1.3
23:18:13: #
23:18:13: ########### PREPROCESSING SCRIPT ###########
23:18:13: #
23:18:13: # Script for mono camera preprocessing
23:18:13: #
23:18:13: # Needs 4 sets of RAW images in the working
23:18:13: # directory, within 4 directories:
23:18:13: #   biases/
23:18:13: #   flats/
23:18:13: #   darks/
23:18:13: #   lights/
23:18:13: # Saves masters to ./masters/
23:18:13: #
23:18:13: ############################################
23:18:13: Running command: requires
23:18:13: # Convert Bias Frames to .fit files
23:18:13: Running command: cd
23:18:13: Setting CWD (Current Working Directory) to 'C:\Astro\M82\biases'
23:18:13: Running command: convert
23:18:13: Convert: processing 120 FITS files...
23:18:13: Conversion succeeded, 120 file(s) created for 120 input file(s) (120 image(s) converted, 0 failed)
23:18:13: Running command: cd
23:18:13: Setting CWD (Current Working Directory) to 'C:\Astro\M82\process'
23:18:13: # Stack Bias Frames to bias_stacked.fit
23:18:13: Running command: stack
23:18:13: Checking sequences in the directory: C:\Astro\M82\process.
23:18:13: Stacking sequence bias_
23:18:13: Processing all images in the sequence (120)
23:18:13: Stacking result will be stored as a 32-bit image
23:18:13: No registration layer passed, ignoring registration data!
23:18:13: Stacking error: input images have different sizes
23:18:13: Opening image 40 failed
23:18:13: Stacking failed.
23:18:13: Stacking failed, please check the log to fix your issue.
23:18:13: Execution time: 7.26 ms
23:18:13: Setting CWD (Current Working Directory) to 'C:\Astro\M82'
23:18:13: Script execution failed.

i’m using 1.2.0-beta2

This is the issue. As suggested in the log, check your input files.

I understand that my input images have different sizes. My darks are all the same as the lights. My flats range from 32091 to about 1000. Same as my flat darks which are in the biases folder. My files were made in the ASIAIR. How do I get around this? Must I put my flats in separate folders (i.e. red, blue, green) as well as the flat darks too?

You must record all your frames with same software in order to get same size.