AutoCAD Civil 3D + Multiple Users on the same computer = Blank Ribbon

For a user that installs Civil 3D 2015 on their computer when they launch will launch the product, everything will work correctly. 

When a different user logs on the same computer and starts Civil 3D 2015, they receive CUIX errors, and none of their ribbons or palettes work.

Please check out this Autodesk Knowledge Article to solve your problem:

http://knowledge.autodesk.com/support/autocad-civil-3d/troubleshooting/caas/sfdcarticles/sfdcarticles/Civil-3D-2015-missing-ribbon-workspaces-palettes-and-support-files.html