Access Denied to .Net folders when processing a SQL 2012 SSAS Cube

We recently migrated to a new server. The deployment went smooth, up unto the point where we had to process the cube. When trying to process, it failed immediately. The error was: "Errors in the high-level relational engine. The following exception occurred while an operation was being performed on a data source view: Configuration system failed to initialize;An error occurred loading a configuration file: Access to the path 'C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config' is denied. (C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config)
Access to the path 'C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config' is denied.."

Access to path? Easy-peasy fix... except it wasn't. I added the service accounts to the admin groups, gave the folders explicit permissions, no joy. Suddenly I felt very silly - such a simple looking problem, and I can't get it sorted? Google yielded no help... So, out of desperation, I yielded to my AD Admin  days, and thought what I would do then... So, to resolve:

• Reset the permissions of the service accounts
• Added the service accounts to a group with the right permissions
• Changed the SQL and SSAS Service accounts to my own account
• Stop and restart the SQL & SSAS Services
• Changed the SQL and SSAS Service accounts back to the Service Accounts
• Stop and restart the SQL & SSAS Services

Voila, it worked :)