It is not clear where or what kind of ListBox you have. Momentman assumed it was on a UserForm. If it is on a worksheet, and if it is an ActiveX control, then you need to preface his Label1 and ListBox1 with a reference to the worksheet they are on. Assume that is Sheet1...
Sheets("Sheet1").Label1.Caption = Sheets("Sheet1").Listbox1.ListCount
If, on the other hand, they are Forms controls, then you would need to do it this way...
Sheets("Sheet1").Shapes("Label 7").OLEFormat.Object.Text = Sheets("Sheet1").Shapes("List Box 6").OLEFormat.Object.ListCount