Counting Number Of Checkboxes Checked

I have 110 checkboxes on a sheet. User checks some of them. After he is done, I need to know the total number of boxes checked. I wrote a simple loop but there is some little error. Essentially I am trying to have Sub go box by box and see which one of them is checked:

With ActiveSheet
b = 0
For i = 1 To 110
If .Shapes("Checkbox" & i).OLEFormat.Object.Object.Value = True Then
a = 1
End If
Next i
b = b + a
MsgBox b
End With