In Dynamics CRM 2011, after adding 'Activity Status' field on the Email Activity form, any email record with StateCode = 1 has the save buttons disabled.
For example, email with status as 'Sent', 'Pending Send' and 'Received'.
If the email is in draft, the problem doesn't occur.
This is a known design issue in Dynamics CRM 2011.
Create a custom field and populate this with the item's statecode:-
var sCode = Xrm.Page.data.entity.attributes.get("statecode").getValue();
Then remove the Activity Status field from Email form
Dynamics CRM Team