lucy24 - 8:26 pm on Aug 9, 2013 (gmt 0)
500 error because the page is not intended for visitors.
I don't see how you get from A to B. A non-public page should be getting a 400-class error-- generally 401 or 403-- unless you've especially configured it so requests get a 500. What do error logs say? For that matter, what happens when you yourself request the page in an ordinary browser?
Does your robots.txt ever mention googlebot by name?