Was this project made in 4.6 or did you migrate it from another engine version? Are you using the launcher or github? Did you make any changes to your code before attempting to open the project?
Have you updated to 4.6.1 or are you still on 4.6.0? Additionally, Can you open a clean project with no additional content or can you not open any projects at all?
We have not heard from you in quite some time. I am marking this as answered for tracking purposes. If you are still experiencing this error, please comment with the requested information.
Can you post your callstack and logs here so I can take a look? Additionally was your project created in 4.6/4.6.1 or was it created earlier? If earlier did it have C++ in it and did you update that C++ to the new coding standards?