What sort of Error is this ?

[Dastard]

well here is the part of my code

Private msngMouseX()    As Single
Private msngMouseY()    As Single
 
 
Private Sub xic_MouseMove( _
    Index As Integer, _
    Button As Integer, _
    Shift As Integer, _
    x As Single, _
    Y As Single _
)
    If (Button = vbLeftButton) Then
        xic(Index).Move (xic(Index).Left + x - msngMouseX(Index)), _
                           (xic(Index).Top + Y - msngMouseY(Index))
 
      Else
        msngMouseX(Index) = x
        msngMouseY(Index) = Y
 
    End If
End Sub

well it runs fine but at run time when i m moving instances of Xic in my workspace here and there .. after some time .. VB prompts as " run time error '9' subscript out of range " ..
and hightlights this line in yellow

msngMouseX(Index) = x

what should i do to get rid of this problem