The problem with the data upload limit for attachments has been fixed. I have restored it to 30MegaBytes. A recent forum software upgrade was responsible for the changed limit. Please accept my apologies for missing this when upgrading the forum sofware, Mabula.
Using multiple dark flats
In the tab 1) Load make sure you select Multi-Channel/Filter Processing all the way at the top of the tab. Then when you load the DarkFlats, make sure you manually select the corresponding filters. So when you load the short duration DarkFlats manually select Luminance, Red, Green and Blue and when you load the longer duration DarkFlats make sure to select the corresponding narrow band filters. The same can be done when loading the masters.