I get this same exact error on one machine trying to build BO's. I have to build my BO's on a particular machine and have for week, not optimal. Another thread said this was a .NET issue, I spent a 1/2 a day trying to repair/reinstall .NET and gave up. I hope my "good" machine never breaks in this way.Since this is the third person with the issue, it is possible it is SF related after all?