Well, in post 3073, you posted your callback address. It is broken but I assumed you did that just to not have the real url posted here.

Just for yuks, do you have a sandbox account you can switch to for testing?

In a while I'll dig out my google and ZC settings and post so you can compare. One other thing, does your host offer the option to NOT run PHP as cgi? So far the only diff I see is that I run PHP as suexec and don't have that box checked as true.