Thank you very much Jamtart for your reply
I am very glad that you replied the post, but the problem still exists

It will disable mouse but the keyboard still controls the presentation and the end user could race on the presentation by clicking the control keys.

I think that I should disable the keyboard control too. On the other side, if I put the action keys to forward and back the presentation by mouse click, one can click them uninterruptedly and shorten the effects up continousely.

Is there any flag or property in the VBA to check that if any effect is running? or any event associated with the beginning and ending of the effects?
In this way, I can override the events to disable and enable the mouse or check the flag in the function associated with the action key.

Thanks in advance for any help