Cannot revise contacts via import

Tried to circumvent this error by completely deleting schooltool via synaptic. Started all over, but the same message appears after defining Demographics and then adding a person.

Where is the ID-data stored? Please indicate what to delete to start with a fresh system. But am also interested in hearing how to clean up a mistaken import as already mentioned.

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Error Details:

Exception

ValueError: ('Duplicate name', 'first_name')

Traceback

File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 132, in publish
  result = publication.callObject(request, obj)
File "/usr/lib/python2.7/dist-packages/zope/app/publication/zopepublication.py", line 205, in callObject
  return mapply(ob, request.getPositionalArguments(), request)
File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 107, in mapply
  return debug_call(obj, args)
Extra information: <schooltool.skin.flourish.zcml_content.FlourishPersonAddView_addStudent.html object at 0xad44c3ac>
File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 113, in debug_call
  return obj(*args)
File "/usr/lib/python2.7/dist-packages/z3c/form/form.py", line 216, in __call__
  self.update()
File "/usr/lib/python2.7/dist-packages/schooltool/basicperson/browser/person.py", line 1007, in update
  PersonAddViewBase.update(self)
File "/usr/lib/python2.7/dist-packages/schooltool/basicperson/browser/person.py", line 987, in update
  self.fields += self.getDemoFields()
File "/usr/lib/python2.7/dist-packages/z3c/form/util.py", line 273, in __add__
  return self.__class__(self, other)
File "/usr/lib/python2.7/dist-packages/z3c/form/field.py", line 136, in __init__
  raise ValueError("Duplicate name", name)

Modules

schooltool 2.8.5 (/usr/lib/python2.7/dist-packages)

schooltool.gradebook 2.8.4.1 (/usr/lib/python2.7/dist-packages)

schooltool.intervention 2.7.0 (/usr/lib/python2.7/dist-packages)

schooltool.lyceum.journal 2.8.2.1 (/usr/lib/python2.7/dist-packages)
Runtime

Python 2.7.6 (default, Jun 22 2015, 18:00:18) [GCC 4.8.2]

Linux vcs_schooltool 3.13.0-77-generic #121-Ubuntu SMP Wed Jan 20 10:50:59 UTC 2016 i686 i686

Filesystem encoding UTF-8, preferred UTF-8

Please see http://book.schooltool.org/database.html

Found out I have to do a full reset of my system (after deleting the database) before the change is noticed. Only restarting the browser wasn't enough. Didn't realize that. Things are OK now. Thanks