I always get the following error message when I try to add a code field to a content type in the section 'Manage display':

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /MYSITE/?q=admin/structure/ds/ajax/add_field/custom_field StatusText: Service unavailable (with message) ResponseText: PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in variable_set() (line 971 of C:\wamp\www\MYSITE\includes\bootstrap.inc).

How can I solve this?