Hello Dedy
I see that you are using some color tweak for the dashboard. Check on combo box properties under display (last tab) and look for color notification.
Also if this doesn't help out, try using new combo box and don't copy the same. Hope this will give some idea.
As Xavier pointed out, does it occur when you just use combo-box on plaint dashboard (test purpose)?
Regards
Kishore Balachandran