I have the following code to open a calendar when I select cell C10

Private Sub Calendar1_Click()
ActiveCell.Value = CDbl(Calendar1.Value)
ActiveCell.NumberFormat = "mm/dd/yyyy"
ActiveCell.Select
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Cells.Count 1 Then Exit Sub
If Not Application.Intersect(Range("C10"), Target) Is Nothing Then
Calendar1.Left = Target.Left + Target.Width - Calendar1.Width
Calendar1.Top = Target.Top + Target.Height
Calendar1.Visible = True
' select Today's date in the Calendar
Calendar1.Value = Date
ElseIf Calendar1.Visible Then Calendar1.Visible = False
End If
End Sub

My problem is that sometimes I open a file with various values that are then
copied to the calendar sheet. One of then is a date for C10. The code fails
because it wouldn't allow copying to this calendar cell

Is there anyway to overcome this problem?