Calling Function from Module to Form got an error Variable not set

[atzdgreat]

just want to know what I missed with these. I'm calling sub from mainwindow

in MainWindow Form

Public Sub ChangeData()
       msgbox("Ok")
End Sub

in Module

Sub PrintIntercept()
       Mainwindow.ChangeData  '------> Here it says that Object variable or With block variable not set
End Sub