I do not believe that the SQL version you are running is compatible with x64 and this only occurred with ACT2011. You could probably update the version of SQL but do you have a specific reason for wanting to run ACTdiag?
Paul Buchtmann email@example.com Australia Australia's First ACT Consultant (1989)
FREE Record History to change default to Call or To-Do for ACT! 2010-2012 versions. Custom versions also available.