Hi,
I updated my WP yesterday to 3.6 (and this morning to 3.6.1).
I then also updated SP to version 5.3.1 (Build: 10616) and all plugins as well.
Everything worked fine.
However, this morning I noticed that the inbox looks different than before:
The inbox now looks like a forum.
When I click on any of the messages, I get a 404 Error.
So, it seems the inbox system is broken. 
How can this be fixed?
Marc
broken?? nah… its a complete redesign of the pm system… db was archaic and almost everyone hated the old pm inbox system…
so we redesigned it…
but of course, 404 errors are not part of the deal… can you try deactivating the pm plugin and then activating it again?
Sorry, I didn’t want to complain about the new design. I also think it looks better than before… 
Have now de-activated and then activated the plugin and… it works now.
Thanks a lot for the quick help!
Marc