hi,
first thing you do is to expose the parent form though properties.
for example
in the CHILD form
//create a properties with the typed of MDIform in CHILDFORM
// frmMainMDI
public frmMainMDI ParentMDI
{
get{return this.ParentForm;}
set{this = value; }
}
call the CHILDFORM like this in MDI form
frmChild ofrmChild = new frmChild()
ofrmChild.ParentMDI = this;
ofrmChild.show()
setting the picture box in MDIFORM:
ParentMDI.PictureBox.Enable = false;