Since the main Office 365 website admin panel is extremely limited (thanks Microsoft), I turned to good old Google for answers. After doing a bit of online research, I eventually found a solution to the account block issue, using some PowerShell commands. Connecting to an Office 365 account via PowerShell wasn’t terribly difficult, thanks to this excellent guide on Phil Wicklund’s blog: http://blog.philwicklund.com/fff/2011/08/using-remote-powershell-to-manage-office-365-identities.html
After getting my PowerShell environment setup, I was able to unblock the affected account easily, via this command:
Unblock a Office 365 Account: Set-MsolUser -UserPrincipalName USERNAME@YOURDOMAIN –blockcredential $falseAfter issuing the command, the affected user was able to logon immediately after. Problem quickly resolved, courtesy of PowerShell.