[Zope] strange form behaviour

Hi I have a form that has a python script as an action in a plone site. If I login to plone as user admin then the script works fine. If I login as user djk@microamps.com the script instead of going to doUpdate as it should, pops up a dialoge box saying open/save doUpdate.com. Logging using an email address is fine in all other aspects and I have been using this with 3000 members for the last year just fine. It has just started happening. Anyone experienced anything like that? TIA Dave