Populating a list box with data from worksheet
Type Mismatch

With Worksheets(CourseSelection).Range("A3")
    Set TaskList = Range(.Offset(0, 1), .End(xlToRight))
End With

frmTaskSelection.lbTasks.RowSource = TaskList

Sub test()
    Dim ws As Worksheet
    Dim rng1 As Range
    Set ws = Worksheets("CourseSelection")
    Set rng1 = ws.Range(ws.[a3], ws.Cells(Rows.Count, "A").End(xlUp))
    frmTaskSelection.lbTasks.RowSource = "'" & ws.Name & "'!" & rng1.Address
    frmTaskSelection.Show
End Sub