Checking Check Box does not trigger peoplecode?

If you have a checkbox that does not trigger a peoplecode., say for example:

If P_DERIVED_IMPT.P_IMPT_CHECK_BOX1.Value = ""Y"" Then
WinMessage(""CHECKED"");
Hide(P_IMPT_TBL.P_IMPT_VERIFIED);
Else
UnHide(P_IMPT_TBL.P_IMPT_VERIFIED);
End-If;

Check on the component properties, if the mode is differed instead of interactive.

Make it "interactive" mode and then it should work.