I understand from the user manual that it is possible to have more than one project loaded at the same time.
So, I loaded the first project and it was working with no problems.
I then wanted to have a look at how another project was set up, so I loaded a second project but did not activate it. No problem so far, but then I attempted to ‘Activate’ the second project - at this point the ‘A Serious Error has occurred…’ message appeared and the system had to be completely shut down.
The second project no longer functions, even if loaded on its own in N6.5.
I did not de-activate the first project before trying to activate the second project (I assumed, maybe wrongly, that activating the second project would automatically de-activate the first project), so there may be a little bug in this area.
I have restored a backup of the second project and it does work properly when loaded on its own, so this would indicate that something in the process described above caused the project to get damaged.
I normally never use the facility to load more than one project at the same time as I had similar issues with it years ago, but I thought that by now any problems in that area would have been fixed.