An instability has been found in Microsoft.NET version 4.0 that is causing unexpected crashes in Autodesk Inventor.
Users experiencing this issue will probably be working with larger data sets and will be presented with either a Microsoft/Autodesk dialog box, or Inventor will simply exit.
Microsoft has fixed the problem in .NET framework 4.5 but a hotfix is available directly from Microsoft.
Please also see additional information here
If you plan to update to the later Microsoft .NET framework please ensure that any business critical applications are supported.