Android 4.0.3 phone doesn't sync calendar up to Exchange 2010 - everything else fine

Hi All,
I have an Android 4.0.3 phone in our organisation that won't sync the calendar from the phone up to our Exchange 2010 (and therefore Outlook 2010). Everything created from Outlook 2010 syncs fine with the phone. Everything created on the phone (except calendar items) sync fine with Outlook 2010. Any event created in Outlook can be edited on the phone fine (including deleting).
The issue occurs only when the user creates an event on the phone - it never appears in his Outlook calendar.
There are no errors appearing in Exchange Activesunc on the phone.
Yes, I have removed the Exchange Activesync and cleared the data/cache from the phone. And then recreated it. Several times. Calendar sync works for a couple of times from phone to Exchange/Outlook then stops. The last time, the calendar never sync'd new items from phone to Outlook at all. Have also removed all other syncs, and issue still persists.
Yes, I have made sure that new entries on the phone are set up using the Exchange calendar and not other calendars on the phone.
As a test, I set up an event on the users Google calendar and it worked fine between phone and Google.
Tried using Touchdown as an alternative, and after struggling to get a connection, it sync'd once and never again (in either direction). It was removed.
We are running a single SBS2011 server on our network. iPhone users don't appear to be having a problem.
Any suggestions as to how to get this working would be appreciated.
Thanks.
Glenn.