.NET Framework 4.0 is required by applications like AutoCAD 2012, AutoCAD Architecture 2012, AutoCAD Civil 3D 2012, AutoCAD LT 2012, AutoCAD Map 3D 2012, AutoCAD Mechanical 2012, Autodesk 3ds Max 2012, Autodesk 3ds Max Design 2012, Autodesk Inventor 2012
Autodesk’s Knowledge Base TS16436702 provides more details:
Many of the Autodesk 2012 products require the installation of Microsoft .NET 4.0. In many cases .NET 4.0 will automatically be installed by the Autodesk 2012 installer however there are system-specific conditions where .NET cannot be installed by the Autodesk installer and will need to be installed manually.
This typically happens on systems running Windows XP without certain Windows updates or Vista and Windows 7 systems that are not up-to-date. In cases where a manual installation of .NET 4.0 is required, you will see the following alert dialog when you click the Install button to begin the the installation process:
Clicking the Update button will automatically terminate your Autodesk product installer and begin the .NET 4.0 installation.
To ensure that the Autodesk product installation is not interrupted by .NET 4.0 installation requirements, we strongly recommend manually installing Microsoft .NET 4.0 before beginning installation of your Autodesk 2012 product.
Note: This is especially important for systems that will be receiving an Autodesk 2012 product via silent installation of a deployment. Deployments will not check for .NET 4.0 and will not install if .NET 4.0 is not present on the system.
Microsoft .NET 4.0 is available on the Autodesk 2012 product media in the following location:
If you do not have access to the original Autodesk 2012 product media, you can download the Microsoft .NET 4.0 installer at the following location (refer to the Microsoft-supplied readme and documentation for additional information and prerequisites):
After .NET 4.0 has been installed, you must reboot your computer. You should perform this step even if you are not prompted to reboot. After your system has restarted, you can begin the installation of your Autodesk 2012 product.