http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_26374879.html
Synchronization with your iPhone failed for 1 items.
The following items couldn't be sent to your mobile phone. They haven't been deleted. You should be able to access them using either Outlook or Outlook Web App.
Item Folder: Inbox
Item Type: IPM.Schedule.Meeting.Resp.Pos
Item Created: 3/08/2010 3:09:25 a.m.
Item Subject: Accepted: Test 4
This not only effects iPhones also had this for Nokia devices. The problem occurs with the Accepted: or Declined: email that come back from booking a meeting with a resource or person. It is related to the unread/read mark.
In my client if I leave these Accepted/Declined messages unread I do not get the "Synchronization with your mobile failed for 1 items" once I have read the message I get the error. Basically what's happening (or not happening) is that the message remains unread on my mobile device. So the unread/read mark is not transferred to the mobile device.
When I then look at the message on the device it says "This message cannot be displayed because of the way it is formatted. Ask the sender to send it again using a different format or email program. text/plain"
If I open an Accepted/Declined message on the device before it has been read on the client it reads fine "Your request was accepted"
It's like reading the message in the client is changing the format of the message some how.