Last week I use Access 2010 open up a 2007 accdb file, and modify some forms and then save it. One of my colleague tell me that he could not open it using Access 2007. It just said the database format is not matching or something like that.
So I search it and find this Backward Compatibility Issue
Backward Compatibility between Access 2010 and Access 2007
Features that are not available in Access 2007
Microsoft Access 2010 introduces features that are not supported in Microsoft Office Access 2007. Access 2007 Service Pack 1 (SP1) will not open databases containing these features; Access 2007 Service Pack 2 (SP2) will in some cases offer limited viewing and designing capabilities. Therefore, installing SP2 will help you access more applications created in Access 2010.There is so much new features in 2010 so Access 2007 won’t recognize it. Then what i did was make a new blank accdb database file and set the [New database sort order] -> [General Lagacy] and then import from the old database. And save it, and then i use an Access 2007 to open that database and then set the password for it.