I have found this post on the web that is similar to my problem. Parsing the following line before parsing the original Xaml is a workaround of the problem that is working for me (as explained in the post). A little bit weird to my taste.
That last link doesn’t appear to work, but the URL text suggests it *might* be a beta-2 problem. Are you confident that you have an up to date (or at least a non-beta) .Net 4?
Hello John, my computer did some 'Windows Update' automatically since I wrote that post and now everything is working fine. I am working on a Window 7 Professional with a .Net version 4.6.2 now.
I agree with you that it is a Microsoft bug, but I still don't understand why the same code was working on my previous v14.1 and not on v15. I am using the following for my 'dyalog.exe.config' file on both version of the interpreter: