Back up Failed Access is denied

• Sql Server 2012 Express
• Default instance (not named)
• Followed this Walkthrough...  http://msdn.microsoft.com/en-us/library/jj219062.aspx
• Installed to Seperate Drive for web.

I have followed this...

• Gave the root directory MSSQLSERVER full access.
• Double checked that the domain user the service runs under has permission as well.

No matter what permission I seem to give it it doesn't work.  

Please, any ideas.  I am under a highly visible deadline pressure and, of course, having to deal with someone else's job.