Q&A: Why can I log into Windows but not the MacOS?

Question:

On the cluster machines, I can log into the Windows operating system, but not the Mac operating system. Why is this?

Answer: 

If you are a visiting scholar you may not have a full-service SUNet account. The MacOS requires the user to have a full-service SUNet account, which gives them web (or AFS) space and most visiting scholars don't have this access. See this page for more information about SUNet IDs.