You need
MouseDown,
MouseUp and
MouseMove. All of them within the
GroupBox. So you need to add this to your form constructor:
public frmChequeFormat()
{
label13.MouseDown += label13_MouseDown;
label13.MouseUp += label13_MouseUp;
label13.MouseMove += label13_MouseMove;
}
Then rename your
gbCheque_* methods accordingly so they get called.
[Edit]
Renamed event and method names above from gbCheque* to label13*
The label shields your groupbox from getting those events. They are routed to the label instead. Hence the renaming in contrast to my first attempt.
Events should still be routed to the label, but now call handlers from there. At least until user moves the mouse very quickly to the upper left so it leaves the label and therefore causes label events to stop firing.
[/Edit]