Hmm, that definitely sounds plausible as a cause to me. I'm assuming you tried continuing to use capital letters everywhere, including the Google auth setup? In theory, if everything matches they should accept it, but it's possible somewhere in their code (or ours), the case is getting lowered automatically, and then it's failing to match up when Google does that URL comparison to see if it's set right.
Perhaps we should have you destroy everything and start over with an all-lowercase subdomain? I am wondering if Sandcats will let you register the same name without capitals as if it's a new registration or not, or if we'll have to fix something there. Perhaps we should see if for the future we can make our installer lowercase whatever you enter before it does anything with it, so that people don't run into this in the future...