@lasse-lindqvist
Hi, thx for the hint however the mystery probably has been solved, but let me explain.
I have a template file last saved with 9.12 which contains ressources my colleague needed.
It seems like he has opened this file with 9.10 and saved the ruleset from there to his disk (? - not totally sure if he just took the cset and made a copy or really opened a 9.12 file with 9.10 as I guess this won’t be possible)
In his project running on 9.10 he loaded the ruleset and other ressources without any problems.
The ruleset he needs does not rely on custom informations - however a custom view was not working properly and that’s where I realized that he’s not on the latest version - then he performed the update.
Once finished the surprise came in and the error showed up once he tried to open the file he just saved minutes ago twice (cause you never know …) …
So, I checked the custom information as you suggested but did not really have a clue what’s the matter as I did not really make sense in this context. But as the custom view was working now and one of the previous save files of the project also opened successfully without a warning he took the pill and started over again to recreate the latest steps. Then he realized that adding the ruleset (he saved once saved with the old version, see above) brought him back the same error again as he tried to add it now …
That’s when we realized that this was probably the reason why the file got corrupt. At least I know now what happened and the it was basically our fault as he had an outdated version but it still surprises me that he could “lock himself out” without a warning. Especially as the ruleset itself has actually nothing to do with custom information here but seems like just was created with a newer version.