[Zope] External Method Problem

[Ben Ocean]

Hi;
I have this external method:

import string, os

user_id, banner_id, page =3D os.environ['QUERY_STRING'].split("&")
redirect =3D=20
"http://www.myaffiliateprogram.com/u/%(user_id)s/t.asp?id=3D%(banner_id)s&p=
=3D%(page)s"=20
% locals()
print "Location: %(redirect)s\n" % locals()

but when I try and instantiate it as an external method I get this error:

Site Error
An error was encountered while publishing this resource.
Error Type: KeyError
Error Value: QUERY_STRING

Troubleshooting Suggestions
=B7       This resource may be trying to reference a nonexistent object or=
=20
variable QUERY_STRING.
=B7       The URL may be incorrect.
=B7       The parameters passed to this resource may be incorrect.
=B7       A resource that this resource relies on may be encountering an=
 error.
For more detailed information about the error, please refer to the HTML=20
source for this page.
If the error persists please contact the site maintainer. Thank you for=20
your patience.

What to do?
TIA,
BenO