Hi Ben,
I saw an almost identical problem on a pc running windows 7 last week and the problem was cured by disabling the UAC (user access controls) - if you're logged in to your pc as administrator then go to control panel and set the UAC to its lowest level (this should basically disable it). The problem is because rFactor automatically modifies some of the files in the game at each stage (when you choose a track to test on, your player file is edited by the game to update latest mod, latest car, latest track etc etc) - the operating system sees this as a security issue and blocks the program from editing the files, hence the game crashes.
Try disabling the UAC and then reboot and try the game - if the files are all installed ok for the game (hint - if you can see them in the track select and mod select lists they probably are) then it should be ok with UAC off.
good luck, please let us know for future reference.....wrighty
Ok thanks much appreciated that rings true as it seams to default back too one of the pre-installed formula everytime. I will give it a go tonight when I get home.