I’ve encountered a similar situation, except I got the error message when I tried to change the access and delegation. It only happened to a certain user though. What I did to resolve this was to convert the mailfile back down to 7, then converted back to 8. This seemed to have worked for me.
Whoever is trying to update the Preferences, i.e. CalendarProfile his/her name should be there in the ACL. The code is looking for preson’s name in ACL. If it’s not there then it returns a “” value.
If your name is not there in the ACL individually, not in a group, then try adding it with Manager access. The update the doc, it would work absolutely fine.
It worked for me today. The issue was happening in 2 DBs and I found there were no Owner assigned in the ACL. Thus they were getting error. After I added my name as Manager and then saved the profile - it worked fine.