Sage registry issue?

I'm having an issue with Sage (for a change). I've got Sage 2009 installed on one pc & use it for one particular client. Tried opening another sage file on it & it threw a wobbly but now when I try to open Sage again it wants to go back to that newer file which seems to be in a newer version. So it tells me I need to update Sage. I don't want to as that will bugger my original 2009 files (client won't be able to open them) so I want to somehow reset it to find my original file. Any ideas? Needless to say I've tried deleting Sage entirely and reinstalling but other than losing a considerable amount of time and patience there has been little effect.

My main pc has Windows 7 & a 64-bit system and refuses to load 2009 despite allowing me to use V11 so no joy there (even with the XP mode). I hate sage.........................

Will be eternally grateful if someone has the magic answer!!