I am currently running Vegas Pro 21 build 108 and I have never encountered .veg file loading problems.
A former associate has passed me an old Vegas project I have requested from him to rework myself. I have no idea what version it was created with but I know that it dates from 2010. I have never previously had any problems revisiting .veg files from previous versions but this one seems to be the exception.
When I try to load it I get into a dialog that says "Deactivation not successful. The program has possibly been deactivated for this device". I hit OK and after a few seconds the dialog reappears and we continue in the loop. Vegas then needs to be terminated in the task manager to get out of this loop. I am working with other projects with no problem.
Sadly no .bak file came with the project files. I have enabled all legacy options in 'Preferences'
Any ideas?