I managed to make it work by not logging in.
Go to the page with the pulldown that has Nutters For Life on it:
https://www.z2systems.com/np/clients/mi ... &test=true
But for user name and password, I made up new ones as if creating a new account. You don't ever have to use it if you don't want, but it's the only way that I found to stay on the right screen. Alternatively, if you have a user name and password already, you should (should) be able to put it in the appropriate fields and still make this work -- I just didn't test it, so it's still a theory.) But whatever you do, DO NOT log in first. Ignore that stupid "If you have an account with us, please login here to donate" instruction cuz that's when the pulldown option for the teams disappears.
Fill in that page above (name, username, password, address, donation amount, etc., including the correct Nutters For Life pulldown option), and hit Submit (which should really say Next, but anyway). On the next screen, you will then add your credit card info, and the money gets credited correctly.
The key: DO NOT DO NOT DO NOT LOG IN.
Dramatic highlights & a unique musical cosmos. Guaranteed.