Comment 1 for bug 783887

Usually this does not happen. I could add, remove custom fields, and everything worked.

One way to reproduce this is:
1. create a second field with Title=whatever, ID=ID
2. try to edit a person, crash (Duplicate name: ID)
3. go to Demographics, remove the first ID.
4. try saving the person again, and you get this InvalidKeyError.

To avoid this issue, delete a field that causes problems. In our test case, it is "whatever", its link ends with "ID-2". Create a new field, but set ID to something else. , e.g. Title=Logon, ID=logon.

The problems are that ID is not checked for uniqueness when creating a field (2), and that ID is used where __name__ should be (4).