I'm guessing the problem both of you encounter has to do with a missing model which is referenced in another model which is unused. In this case the missing model validation will not appear if you've left the validation preferences with their defaults.
I have managed to replicate such a scenario, but still feel it would be useful to have a look at your models. If you do not want to post these models in the forum, I would be happy to receive them by mail. If you wish me to contact you directly, leave me a note via the Contact Us page.
For best results, use the Firefox browser..