I have started to deploy Crystal Reports SP21 to my users.

One very strange behavior I found is an unhandled exception (Could not load file or assembly CrystalDecisions.CrystalReports.Engine, Version=13.0.3500) is triggered when trying to load a report. I am sure that I have done everything correctly just like I did for prior versions.

But this time, even after all my usual magic tricks, I still had this error:

What I found to fix my issue was to repair the installation of "SAP Crystal Reports runtime engine for .Net Framework". Not a re-install, really a repair from the "Programs and Features" dialog.