language incompatibility using Runtime licence

[mikelane]

I have completed my database, purchased the developer edition of Office XP for the Access RunTime licence and started to distribute it using the packaging tool that comes with |Access Developer. Several people are getting this error message when they install it. "The Office system pack can't be installed on this system. The language is not the same. Install the office system for the appropriate language on your computer."
I have specified English as the language during the packaging process and their machines appear to be setup as English.
Any ideas what thi smeans and which language settings I change?
Thanks Mike