After deleteing a group, adding contacts fails with DB constraint error

I have the following problem. I deleted a group and now I cannot add any more contacts. I keep getting this error. How can I solve this.

DB Error: constraint violation

message. The full message is:

REPLACE INTO civicrm_group_contact ( group_id, contact_id, status )
VALUES
( 1, 90, ‘Added’ ) [nativecode=1452 ** Cannot add or update a child row: a foreign key
constraint fails (vlaanderen_wordpress.civicrm_group_contact, CONSTRAINT
FK_civicrm_group_contact_group_id FOREIGN KEY (group_id) REFERENCES civicrm_group
(id) ON DELETE CASCADE)]

Fatal error: Uncaught CRM_Core_Exception: [0: Transaction integrity error: Expected to find active frame thrown in /home/vlaanderen/www/www/wp-content/plugins/civicrm/civicrm/Civi/Core/Transaction/Manager.php on line 93