Tried changing the version manually but it did not seem to help. Aparently one of my friends have had this problem fixed, so I will ask him when possible. Edit: He said he found a fix, but never actually tried it. It didn't work, so back to not knowing how to fix this. Hoo-ray. Edit2: So, what I did...

I've uninstalled Steam and installed it again, still same problem. I even tryed on my laptop same problem there. Since you mentioned registry is there any way to manually enter the CD key there? Or is that mission impossible? EDIT: I also installed AOE3 again Yeah, I actually had the same idea, ent...

Welp, just gonna say that I have exactly the same problem, so if anybody every finds a way to fix it, I'd like to know.