Database error in onepage checkout

[rokoso]

When new customer fills the delivery address in onepage checkout a database error occurs. Switched to classic checkout for now as the correct shipping service do not appear after filling address. When you go back to one of the address fields and change something (like one digit of the post code) then it continues to the shipping service. Saw the error in Chrome with developer tools, here it is:

Could not execute query [Native Error: Cannot add or update a child row: a foreign key constraint fails (domain_database/CustomerOrder, CONSTRAINT UserAddress_CustomerOrder FOREIGN KEY (billingAddressID) REFERENCES UserAddress (ID) ON DELETE SET NULL ON UPDATE SET NULL)] [User Info: UPDATE CustomerOrder SET shippingAddressID = '51768', billingAddressID = '51768', eavObjectID = NULL, shipping = 'C:5:"ARSet":1302:{a:1:{s:4:"data";a:1:{i:0;C:8:"Shipment":1253:{a:6:{s:4:"data";a:11:{s:2:"ID";C:13:"ARValueMapper":2:{N;}s:7:"orderID";C:21:"ARSerializedReference":61:{a:2:{s:5:"class";s:13:"CustomerOrder";s:2:"ID";s:6:"150163";}}s:17:"shippingServiceID";C:13:"ARValueMapper":2:{N;}s:17:"shippingAddressID";C:13:"ARValueMapper":2:{N;}s:12:"trackingCode";C:13:"ARValueMapper":2:{N;}s:11:"dateShipped";C:13:"ARValueMapper":85:{C:22:"ARSerializableDateTime":50:{a:2:{s:10:"dateString";N;s:6:"isNull";s:4:"true";}}}s:6:"amount";C:13:"ARValueMapper":2:{N;}s:9:"taxAmount";C:13:"ARValueMapper":2:{N;}s:14:"shippingAmount";C:13:"ARValueMapper":2:{N;}s:6:"status";C:13:"ARValueMapper":2:{N;}s:19:"shippingServiceData";C:13:"ARValueMapper":2:{N;}}s:7:"itemIds";a:1:{i:0;s:6:"280109";}s:22:"availableShippingRates";O:15:"ShippingRateSet":2:{s:8:"_rates";a:1:{i:0;C:20:"ShipmentDeliveryRate":318:{a:9:{s:13:"amountWithTax";s:4:"2.95";s:16:"amountWithoutTax";s:4:"2.95";s:9:"serviceID";s:1:"1";s:11:"serviceName";s:30:"ДоÑ�тавка в СофиÑ�";s:10:"costAmount";d:2.95000000000000017763568394002504646778106689453125;s:12:"costCurrency";s:3:"BGN";s:9:"className";N;s:12:"providerName";N;s:11:"rawResponse";N;}}}s:14:"_rawResponse";N;}s:14:"selectedRateId";s:1:"1";s:8:"isLoaded";b:0;s:19:"customSerializeData";a:0:{}}}}}}' WHERE (CustomerOrder.ID=150163)]