iCloud Reminders issue 2007 Outlook

Hi everyone. I am attempting to synchronise our work calendars and reminders throughout our workplace and so far the apple icloud has been the best solution, especially for calendars. However we have an issue when creating reminders (outlook calls these tasks) within outlook and having those reminders (outlook:tasks) updated from outlook to icloud on a certain shared reminders list.

Background on devices used,

Dad has a windows 7 Laptop with an iCloud account and Outlook 2007,

I have an imac with mavericks and the standard reminders program bundled.

Here is the issue:

As default, everyone has a certain reminders list. Mine syncs with all my icloud devices.

I also made a second list, that is shared with other icloud users.

My dad is one of these users and has 'accepted' the invitation.

He has icloud control panel on the PC, and we have the reminders (tasks) working in excel.

I can make a reminder on my mac (MWDB Reminders is what the list is called), and it will transfer to his shared reminders on iCloud (MWDB Remidners)

The icloud then sends this reminder from the list to his PC in outlook. It works as intended.

He can make a reminder in the web browser portal in MWDB reminders and it will update onto my mac and also his PC in outlook.

He can make a remidner (task) in outlook and it will NOT upload to the icloud web interface, nor my PC.

I then decided to test it on his other (default) list. This list is a personal list that everyone gets with their icloud account and is not shared by default.

I can make a reminder in his web portal list and it will udpate Outlook

I can make a reminder in his outlook and it will update in the web browser.

Therefore this is the issue: For some reason, icloud will accept reminders (tasks) updloaded from outlook into icloud on his own personal list, but in the shared list (MWDB Reminders) it will not update to icloud. He can receive and view reminders (tasks) on this list but not make new ones, nor tick them off.

So my conclusion is this: He must not have permission to add, update or delete reminders from outlook in this shared list. It works on the icloud portal, but not outlook. Why is this so? How come he can add, delete and update reminders from his own personal list from outlook but not this shared list (of which I am the owner)?

Any help woud be appreciated guys! Thanks!