My colleague and I are at a loss with this. We've had a company look at the problem and they are at a loss too.
We had exchange 2007, upgraded to 2013 in the summer of 2013 and migrated all the mailboxes, public folders and shared calendars across. Everything was fine until the people who should be able to edit the shared calendars couldn't. New appointment button was greyed out. They all have permission to do this, however it's not working.
It's really intermittent too. You would close Outlook (2010) open it and then it works, and then close it again and it stops working. Sometimes even stops working when your working on it.
Exchange is virtualized and Hyper-V being the hyper-visor. The server it's on is a 2013 Server too.
It's been driving us nuts, and the company said that they've had to let Microsoft know of the issue, but it might not even get addressed.
All I'm looking for is a step for a hint or maybe even an alternative to it all?