If you ran setup from the web path mydomain/zenphoto it would have changed the webpath to "zenphoto" so you have not done this correctly. Things may work (but not mod-rewrite) with a wrong base, but certainly there will be issues.
You might want to install the support release. Your error line number does not correspond to any line in that release, which is all I have access to while I am traveling, so I cannot speculate on its cause.