Performing field validation at END button on IC toolbar with CRM 2007

Hi friends I need some help with END BUTTON on IC toolbar with CRM 2007.

My problem is, clicking on button END all documents (activities) are automatic saved and closed, but the mandatory fields are not validated.

What I need is, clicking on button END the system have to perform before all screen validation for mandatory fields, in case everything OK, save and close all documents (activities), otherwise cancel this action.

Does anybody know if there is a way to do this?

Regards,

Lalas