The recent IDE updates introduced a few changes that Arbed didn’t handle, yet.
I should now have it all fixed.
Would those using Arbed occasionally please download this beta version and let me know if Arbed reports any troubles opening your project(s):
Nothing critical. Just the information we already mailed about 
Oh, I had forgotten about your report. Thanks for the reminder.
New version 1.8.6 is available now, supporting project format changes in Xojo 2016r4 or 4.1.
See here: http://www.tempel.org/Arbed/
I highly recommend everyone to get a copy of this app.
http://mbs-plugins.de/archive/2016-12-30/Arbed_186_updated_for_Xojo_201/monkeybreadsoftware_blog_xojo