Windows 7 Lost Profile

This morning was filled with angst and emotion. We had a great evening with friends last night watching the meteor shower (even though the kids fell asleep at 11pm). 
And after a beautiful drive to work in the sunshine, a free coffee on my desk (from a grateful staff member I had helped yesterday) and no-one running screaming 'HELP, THE WHOLE INTERNET IS DOWN!!', I sat at my desk to be greeted with this;

Windows Cannot Load Your Default Profile. Access Is Denied. Event Error 1505.

What?

(now I know I sound a little like the 'Doctor', but WHAT???)

Sigh.

Luckily, this issue has occured on both Vista and Windows Server 2008 machines too, (mine is the fantastic Windows 7, and yes, I Am A PC... but I digress...) and someone had posted the solution. I would love to link to it for you however, I dont have access to the temporary profile. I can tell you I found it on the Tek-Tips forums after a brief google search.

The Solution (for Me):

Open RegEdit, and navigate to the following key folder;
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList

The profiles are stored in folders with the SID of the user as their name, however my profile was appended with a '.bak'

All I did, was remove the .bak from the folder name and logoff/logon.

Why Did it Happen?

I got nothing.