Although I'm using LXDE I'm posting this here because I doubt the desktop has anything to do with it, and it may help others using KDE.
Dropbox - I've been using it now on three computers in two different locations for about four months. And basically it's been excellent and I've really come to depend on it. However, yesterday on one computer, it wouldn't launch automatically as I've configured it to with Parcellite in /home/me/.config etc. Not only that, but starting it via the menu it wouldn't connect with the server and timed out after 30 seconds and disappeared. I've tried uninstalling and re-installing - no joy. Plus I've unlinked that computer via the Dropbox website and re-linked it. As far as the site is concerned, all it as it should be. But still it falls over in exactly the same way.
Now, whether the following has anything to do with it, I don't know. And that is that yesterday also in that location - and I can't relate the timings to each other - I changed the router I'm using. I didn't at first see on the face of it what that would have to do with it - unless the gateway address is relevant and the two routers have different ones - but in any case I put the original router back and that's had no effect. On my main computer I also had to re-link it (so I guess the router may be a factor) and having re-linked that machine it's now working fine.
Sorry if that all sounds a bit convoluted, but if anyone can suggest any way around this I'd be very pleased.