Microsoft Project told me about the error when I almost finished editing one very large file. I thought that I saved everything successfully, but after this failure I could not open the file with my work and didn't see my last data. The error is the following: "Project can not recognize this file format. Do you want to open this file only as text?" Trying to open this file from another computer was with the same result. I don't know how to cope with this terrible problem.