How do I make my Outlook 2007 calendar running on Windows 7 sync with my iPhone 4s and iPad? It's stopped syncing

I've already downloaded the iCloud app to my Windows PC and have ensured the check box is ticked next to mail, calendars, etc.

I've also gone into Outlook settings Tools>Trust Center>Add-ins and the iCloud Outlook add-in is listed under the Active Applications Add-ins list.

I'm not sure what else to check. My work system (windows) also run Netbox as a security system - would that have anything to do with it? I'm clutching at straws so any advice would be greatly appreciated.