I have several times had problems with the Microsoft Project file and I was able to solve these problems. But this time when I saved it and then tried to open it I received a message that the file is doesn't open. I looked in the properties of this file and size its has not changed and it weighs 850kb. This file was sent to me. It was created in Microsoft Project 2010 and then saved in Microsoft Project 2007. How can I restore it?