Files are sometimes read only

I have a small 2011 Essentials server with 6 people attached to the domain.  There are two shares one for a Access application and the other is a large share with all user documents and CAD files.  All the users have full access to each share and i have checked this time and time again.  All users have Office 2007 installed and all updates have been installed and all updates have been installed on the server.  When a user access a document from the share makes changes and wants to save the document, the message appears that the document is read only and they have to rename as a different document.  I know this is not the normal because I have users on 2008 servers with Office 2003, 2007 and 2010 and I have now issues.  Can someone shed some light and point me in a direction to resolve this issue for this customer.