RTC permissions on Item Journals

I have a user that is allowed to post in the Item Journals in the classic client. In RTC the form does not open, no error message is shown. I guess the are doing the same thing and permissions should not have to be extended just because he is using RTC?

I added permissions table 82 and 83 and synchronized this users permissions. No results from this change. He has excecute permissions on all pages.

Any ideas on how to find what is missing? I saw the "User Rights Setup" tool, but this doesn't work for RTC nor Windows logins according to the documentation.