When looking at their computer I notice a script error in IE:-
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.3)
Message: Library not registered.
It seems that when Outlook 2003 was uninstalled and Outlook 2010 was installed a dll gets unregistered and not re-registerd again. The file is called name.dll.
So to Fix:-
In CMD navigate to:-
C:\Program Files (x86)\Microsoft Office\Office14
And run the following command:-
Then close all IE windows and try it again and all should be good.