404 Error for Isolated Users in Dynamics CRM

I had an issue recently where one user was getting a 404 error when trying to log into CRM. While troubleshooting this issues I tried everything I could think of, including disabling Local Security Authority (LSA) credential caching on the ADFS server, recreating the user's Active Directory account, disabled/re-enabled her CRM account, purged her kerberos tickets, deleted her cookies, killed her ADFS sessions, rebooted servers, reset passwords, checked her security roles, etc. After trying every perceivable resolution, this is what I had to do to fix the issue.

1. Changed the logon account for the affected user to an unrelated service account that wasn't used in CRM, and disabled the CRM account.
2. Created a brand new account for the user in CRM, and assigned the security roles that the old account had.

Hopefully that works for you too.