[Zope] can't add back "title" to object?

I've got a folder from which I (mistakenly) deleted the "title" property. When I try to add it back (title / string / <string value>), I get a Zope error: "Bad request / invalid or duplicate property id". This is probably a Zope-for-Dummies-style question, but I'm a little stumped. (A quick Google search turned up nothing, though perhaps I'm not looking correctly.) Thanks for any help. -- Cheers! Chris Ryland Em Software, Inc. www.emsoftware.com