For some reason whenever I try logging on with my MacID and password, either google or MUSS says it's invalid. I've tried many times with the same results, with the info I use to log onto mugsi all the time.

it says "invalid email; we are unable to process your request at this time"

and actually gives me an option to sign out at the top right corner.

Assuming you've been logging in through the Mcmaster gmail portal, not just the google one and having this issue, you could ask University Technology Services (http://www.mcmaster.ca/uts/)

Did you activate mac id?
http://www.mcmaster.ca/uts/macid/

Did you activate the services?
Go to mugsi>log in>My Mugsi>Profile>Activat e mac id services. Wait 24 hrs to activate

I had the same problem. You have to activate your mac id services. You can sign on again within 24 hours