Thank you for your answer!
Also in any backup file there occur errors… What do you mean with “if both machines are different”?
I also set back the package versions back to the versions that were used when developing this, but the errors are still there.
And by the way, in the beginning of December, the used package versions worked. And without doing any changes, now by opening the project there are a lot of errors… 
I’m at a loss…