Marking throws error (Bug #572)

Hello
I am using AMC since many years and i am very happy with it.
I may have a bug....
I am using theses versions:
This is AutoMultipleChoice, version 1.4.0~beta2 (r:4cf8d48)
Perl: /usr/bin/perl v5.26.1
When I try to mark the scanned pages, marking process runs, but in the log I see the error message:
Can't call method "set_type" on an undefined value at /usr/share/perl5/AMC/Scoring.pm line 186.
Marking doesnt finish properly and I cannot continue to export data...
I dont know how to solve this error ... Maybe you can help me.

Maybe this can be helpful: when I created the project and layout I used Ubuntu 14.04 version (with latex and amc versions shipped) and in the meantime i upgraded to ubuntu 18.04 and the upgraded latex/am versions. Maybe this is correlated to that?

I attached the AMC log file.

Best thanks for any help.