I highly doubt any of this would be an issue as this is maybe a 2/10 the most ridiculous/complex/huge craft I've ever launched in this game and I've recently upgrade from a 6 y/o laptop to a pretty decent desktop so I've gone away with any calculation errors/glitches and its such an oddly specific error. I'm thinking it more has to do with them being direct attached to other boosters and it doesn't like that as an attachment. I'm going to play around with this some more in the morning when I have energy and keep this thread posted with what I find.
Also yes I know I can orbital refuel but that isn't as fun and I see no reason why I shouldn't be able to launch the 3,000 part 50,000 tonne mechazorb rocket if I feel so inclined to turn my computer into a space heater