stalefries said: I think that before we try this we should understand what's happening each time it gets launched. For example, mejy said that launching from the terminal, from a panel launcher, and from the menu bar all work.
When launching from the terminal, one only uses "epiphany". In the other 2 instances, I believe they use "epiphany %u", the "%u" allowing you to, for example, drag some sort of file or url for epiphany to open onto the icon.
This is where my knowledge of these things stops. How does USP launch it? I think deskbar uses some sort of dbus method to communicate to epiphany, but you said that you don't. And what about SLAB?
AFAIK, %u is generally the first argument passed to a menu item/launcher etc (ie. anything dragged onto it), and if the argument is empty, as is the case is nothing is dragged onto it, then "%u" will be converted to "", so the launch command will simply end up as "epiphany". (Or atleast that's how it would work with C++/Windows - I'm not too sure about Python/Linux).
Also, removing %u with alacarte or manually at /usr/share/applications/epiphany.desktop has no effect on the error.
Does anyone know of any other d-bus applications, so we can tell if it is d-bus or epiphany at fault? Also, seeing as running it from the terminal, is USP using a non-standard method to launch epiphany? One more thing - alt+f2 epiphany works fine to.
Important EDIT: In deskbar-applet, 'Execute epiphany' causes the error, but 'Launch Epiphany' doesn't.