Just an quick update for customers running AutoCAD 2013 and using any flavor of .NET 4.5.
NOTE: They are both NOT supported but one plays better with AutoCAD 2013. It is best to use .NET 4.0.
Microsoft® .NET Framework® 4.5 Beta
Please uninstall the Microsoft® .NET Framework® 4.5 Beta and install the .NET Framework® 4.5 Release Candidate version.
Microsoft .NET Framework 4.5 Release Candidate
NOTE: Thanks to Alison Gangler for sharing this tip with the community.