For Information in case someone else has the same problem.

I installed the following:
Desktop Manager v3.6 SP3a (Vodaphone)
OS4.0 for 7230 (Vodaphone)

Started Desktop Manager no problem but when I connected the Blackberry it resulted in an error popping up and it never connected properly with the program

I then installed Desktop Manager v4.0 (Blackberry Site Download) over the top.

Now everything works, I have the option for Blackberry Wireless Sync which I chose for the Calendar and now I am able to accept/decline meetings as well as invite people to new meetings/appointments which also wasn't an option before.

I am not sure why I was unable to do any of this when installing Desktop Manager v4.0 originally but I am just glad it is working now.