How do I register a user?
apparently , there is a field of that name ... and some node / entity which is trying to get saved automatically. Could you have Profile2 installed ?
Did you try the report on admin/reports/fields ?
If you dont find it there, try the database - finde the table that uses the column ie this way :

SELECT * 
FROM INFORMATION_SCHEMA.COLUMNS
WHERE COLUMN_NAME = 'field_published_value'
AND TABLE_SCHEMA = 'yourdb'


i tried on a "default install" and didnt see it :)