I can't say I've had any issues with starting the Citybus 200 myself. If you have applied it in the past but it was a while ago, it might be worth re-doing as when Steam updates OMSI - or you run a Verify Integrity - then I believe it can replace the patched 'omsi.exe' file with the original unpatched one.
That usually solves a lot of 'white out' problems. Simply run the program and select the 'omsi.exe' file in your main OMSI folder.
If you are a member of the FellowsFilm website then you can download it here, otherwise you can get it from the official website here. Do you have the 4GB patch installed? If not, that usually helps. Things turning white is usually a sign of memory issues.
