Leonardo, try Purusothaman's solution first.
If it doesn't help, restore your site from the back up ( if you have one).
If you don't have one, make a back up of your site before following further instructions ( you can use "Data Exporter" plugin for this).
Once you are sure that you do have a back up:
Log in to phpMyAdmin>>find "base_question" table >> click the SQL
button in the main menu>>insert this query and click go.
INSERT INTO `%%TBL-PREFIX%%base_question` (`id`, `name`, `sectionName`,
`accountTypeName`, `type`, `presentation`, `required`, `onJoin`,
`onEdit`, `onSearch`, `onView`, `base`, `removable`, `columnCount`,
`sortOrder`, `custom`) VALUES
(112, 'relationship', 'f90cde5913235d172603cc4e7b9726e3', NULL,
'select', 'multicheckbox', 0, 1, 1, 1, 1, 0, 1, 1, 7, '[]'),
(84, '9221d78a4201eac23c972e1d4aa2cee6',
'47f3a94e6cfe733857b31116ce21c337', NULL, 'text', 'textarea', 0, 1, 1,
1, 1, 0, 1, 0, 0, '[]'),
(83, 'c441a8a9b955647cdf4c81562d39068a',
'47f3a94e6cfe733857b31116ce21c337', NULL, 'text', 'textarea', 0, 1, 1,
1, 1, 0, 1, 0, 1, '[]'),
(81, 'password', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'text',
'password', 1, 1, 0, 0, 0, 1, 0, 1, 2, '[]'),
(104, 'realname', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'text',
'text', 1, 1, 1, 0, 1, 0, 0, 0, 3, '[]'),
(94, 'sex', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'select', 'radio',
1, 1, 1, 1, 1, 0, 0, 1, 4, '[]'),
(82, 'email', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'text', 'text',
1, 1, 1, 0, 0, 1, 0, 1, 1, '[]'),
(111, 'match_sex', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'select',
'multicheckbox', 0, 1, 1, 0, 1, 0, 1, 1, 6, '[]'),
(92, 'birthdate', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'datetime',
'birthdate', 1, 1, 1, 0, 0, 0, 0, 0, 5,
'{"year_range":{"from":1930,"to":1992}}'),
(80, 'username', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'text',
'text', 1, 1, 1, 0, 0, 1, 0, 1, 0, '[]'),
(119, 'joinStamp', 'f90cde5913235d172603cc4e7b9726e3', NULL, 'select',
'date', 0, 0, 0, 0, 1, 1, 0, 0, 8,
'{"year_range":{"from":1930,"to":1975}}');
