I've had that before.
All I do is exit Trainz, Start Trainz and wait for at least 1 or 2 minutes before clicking on Driver / Surveyor. You will noticed some birds flying around the menu screen, this gives me an indication the game is fully loaded correctly, then I click on Driver / Surveyor
In TRS22 and Trainz Pluz, the birds are seen around the 2 large white buildings and as soon as you see the 4th or 5th bird flying over the top of the bridge
Then you will know the game is loaded correctly... Now, I'm not sure why! But it has always worked for me