Please read this FAQ:
http://www.webyog.com/faq/content/8/159/en/how-do-i-define-timestamp-properties-with-sqlyog.html
The first “TIMESTAMP NOT NULL” in a table is automatically becoming “”TIMESTAMP NOT NULL DEFAULT CURENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP”. This is like this in MySQL since version 4.1 for compliance with earlier versions. So what you need to do is smply the check the NOT NULL checkbox and *nothing more* (ie. do not set a default explicitly)