TypeError: get_field() takes exactly 2 arguments (3 given)
It will look something like this:
Error Type TypeError Error Value get_field() takes exactly 2 arguments (3 given)
If you get this error when trying to add a Plone site in your Zope, it means that you have a version mismatch somewhere - either running Plone 2.0 on CMF 1.5 or Plone 1 on CMF 1.4 or something else entirely.
Check all your package/product versions, and make sure it is a valid combination. The Plone Core tarball always ships with the correct dependencies, use that as reference if you are not certain which version combinations are valid.