When you say "blank", do you mean absolutely 100% white with no text on it whatsoever? Or do you see some of the Tiki modules/site layout? I assume you don't get any error message such as "you don't have permission"?
I've never seen the 100% blank white page for contact us, only with searching.
You might want to check the tiki_p_messages permission for anonymous users just in case, but it doesn't sound like that's the problem. Otherwise I'd suggest what Gary said, if you haven't done so already.
What you are trying to do is absolutely achievable because I do it all the time, something is wrong somewhere.