You the man 
Changed the Dim NoOfPages as you have to String and added in an ElseIf and it works great now. Many Many Thanks.
Dim counter
Dim NoOfPages As String
NoOfPages = InputBox(Prompt:="Enter the number of additional pages you need", _
Title:="No. of additional pages", Default:="Enter number here")
If Not IsNumeric(NoOfPages) Then
MsgBox "You must enter a numerical value."
ElseIf NoOfPages > 30 Then
MsgBox "Only a maximum of 30 additional pages may be added."
Else
For counter = 1 To NoOfPages