Hmm, well this is a pretty unsatisfactory conclusion.
My module “flo”, was a symlink in my modules folder.
Just doing in Application.cfc generated the same error. (string out of bounds). So it was nothing to do with CB.
As soon as a copied “flo” instead of symlinking it – everything worked.
Funny thing is, all of my modules are symlinked – so I have no idea why it doesn’t like that particular one…
It probably wants you to spell it “flow”. 
I tried that! Seriously I did – lol - I was willing to start typing whilst standing on my head next!
Heh. That’s awesome. 