Output and Math Precision

[wey97]

Option Explicit
 
Private Sub Form_Load()
    Dim d As Double
    d = CDbl("999999999999999.01")
    d = d - CDbl("999999999999999")
    MsgBox d
    MsgBox 0.0000000001
    MsgBox CDbl("99999999999999999999999")
    MsgBox Sin(CDbl("99999999999999999999999"))
End Sub

Why does the first msgbox not output with any precision
when the second does?
Sin takes a double as an argument, so why does the last
statement give an error?