Tf2 validating error
If this fails, or Windows is having trouble closing the game with this method, try restarting your computer.For other operating systems, try restarting your computer.
This system DOES NOT support the Open GL extension GL_APPLE_flush_buffer_range.
This system supports the Open GL extension GL_ARB_map_buffer_range.
Once your computer restarts, perform any troubleshooting operations that you intend before attempting to launch the game again.
After the last update, starting the game shows a black screen (menu music and button presses can still be heard) making the game totally unplayable.
With that knowledge alone I was able to make decent progress.