I can use this verb in the Python Windows SDK. But not in production. Why? What am I doing wrong?

The error message includes (only seen via firebug or fiddler)

Malformed request

or something like that

My code looks like:

from google.appengine.ext import db
from google.appengine.ext import webapp

class Handler(webapp.RequestHandler):
   def delete(self):
       key = self.request.get('key')
       item = db.get(key)
       item.delete()
       self.response.out.write(key)