Add "timestamp" type for MySQL
Like Gian says, you can't have a default value of CURRENT_TIMESTAMP for an int field.

Due to Drupal's database abstraction layer timestamp is not a supported field type. 

This is due to not all databases supporting timestamp or now() as a field default value as apposed to mySQL where it is supported. The solution / work around if you're using mySQL is to add a query to your .install that modifies the field default to now() where the field type is int. See the Data Type doc page for further discussion: http://drupal.org/node/159605 or see here for more info on Drupals DB Schema: https://api.drupal.org/comment/48593