Any WLM 9.0 UIfile will only work under WLM 9.0. It is not backwards compatible nor will it be compatible with say wlm 9.5 or 10 (the next major version)
The same goes for 8.5. 8.5 UIfile code is for 8.5 only.
I've explained the reason why it is like that so many times that i can't be bothered now
so if you really wanna know just look at my tutorial thread.
http://shoutbox.menthix.net/showthread.php?tid=79906
*Also even if you didn't touch UIFile code and only did image replaces it won't work properly since 9.0 has a lot of image ID changes.