[TippeX]

Whats the securom error then? more info helps, we arent all mind readers, and updating and then downgrading the exe probably inst a good idea..

Im guessing you downloaded a "less than legal" version, then bought a serial (cheaply i imagine..or cheaper than the game store price), but the update updated the game, which then made it do the disk check..which wont pass beecause you haven't got the original disk...

If the above guess is right, your only option is to contact the publisher and ask for a disk..
i'm not sure if they will help in this case as you technically didnt buy the game.... only a serial..