Iconpackager - Icon Size Issue

Sorry if this has already been mentioned however I cant resize my icons using iconpacker like I used to when I used XP

Details:

OS: Windows 7 64bit

Iconpacker Version: 5.1

Problem: IP5 working for all options normally apart from the ability to resize my icons. Under Windows Settings, the "use large windows icons" checkbox is greyed out. The Windoes icon custom size is likewise inaccessible with a greyed out box

Assistance would be appreciated