startx broken after update.

So, you boot to a command prompt and use 'startx' to, well, start X. You have more than one desktop installed, e.g. kde and fluxbox, and when you 'startx' you're default desktop, say kde, starts up.
Great. That is until you update fluxbox and kde nolonger seems to work!
If you get errors along the lines of:

	xsetroot: unable to open display ''
	xset: unable to open display ""
	xsetroot: unable to open display ''
	startkde: starting up...
	ksplash: cannot connect to X server
	xprop: unable to open display ''
	kdeinit: aborting. $DISPLAY is not set
	ERROR: couldn't attach to DCOP server
	startkde: shutting down
	startkde: running shutdown scripts
	xprop: unable to open display ''
	startkde: done
				

and you can do things like start fluxbox, open up a terminal and start kde then your problem MIGHT be that fluxbox has been set as your default desktop.
To change back to kde run the following as root:

update-alternatives --config x-session-manager

Then select the appropriate desktop.