Problem: When your game displays a message box saying “Space Engineers cannot be started in 64-bit mode”
Reason: 64-bit version of .NET Framework cannot be loaded
Solution 1: Use the Microsoft .NET Framework Repair Tool: http://www.microsoft.com/en-us/download/details.aspx?id=30135
Solution 2: Uninstall all the .NET frameworks from your computer by going to the Control Panel – Uninstall a program and removing all versions of .NET Framework. Then install .NET 4.0 again from this URL: www.microsoft.com/download/en/details.aspx?id=17851
Solution 2: Install all Windows updates for .NET and security. Reboot your computer if required by the updates. Then install .NET 4.6.1 again from this URL: https://www.microsoft.com/en-us/download/details.aspx?id=49981.
Solution 3: Use a 3rd party .NET Framework repair tool: https://blogs.msdn.microsoft.com/astebner/2008/08/28/net-framework-cleanup-tool-users-guide. This method will fix any broken .NET configuration.
Last resort solution: We have received some reports that reinstalling Windows can be helpful. Use this as your last resort and at your own risk.
If you find what is specifically causing this issue, please contact us on firstname.lastname@example.org. We’d be happy to create a workaround for Space Engineers or provide the tools to fix it automatically.