there is a whole prescribed method.....
it starts in an unlikely way...and then finishes as one would expect...
one most remove the material libraries...in reverse order of installation...
1. Click Start menu (Windows) > Settings > Control Panel.
2. In the Programs and Features select.
Autodesk Material Library Base Resolution Image Library 2015 then click Remove/Uninstall.
Autodesk Material Library 2015 and click Remove/Uninstall
AutoCAD Civil 3D 2015 and click Remove
Autodesk Storm and Sanitary Analysis 2015 and click Uninstall
Autodesk Material Library Base Resolution Image Library 2013 then click Remove/Uninstall
Autodesk Material Library 2015 and click Remove/Uninstall
AutoCAD Civil 3D 2013 and click Uninstall/Change
Autodesk Storm and Sanitary Analysis 2013and click Uninstall
4. Click Yes when prompted to confirm that you want to completely remove the application and all of its components.
5. If you are prompted to remove shared files, click No to All, and then click Yes when prompted for confirmation to proceed.
6. After the uninstall procedure has completed, click OK and restart the computer.
then....
. Using Windows Explorer, delete the following Civil 3D 2013 installation folder:
Windows XP: C:\Program Files\Autodesk\AutoCAD Civil 3D 20xx
Windows XP, Windows Vista, and Windows 7 (64-bit): C:\Program Files\Autodesk\AutoCAD Civil 3D 20xx
and still....
HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R20.0\ACAD-E000:409
HKEY_LOCAL_MACHINE\Software\Autodesk\AutoCAD\R20.0\ACAD-E000:409
Close the Registry Editor.
Restart the computer.
http://knowledge.autodesk.com/support/autocad-civil-3d/troubleshooting/caas/sfdcarticles/sfdcarticles/2015-Resolving-installation-issues-with-a-clean-install-of-AutoCAD-Civil-3D.html
