I get that a lot in the UV editor Jay...the simplest way to do it is have incremental save turned on and then just CTRL S to save then you will be able to select the edges again. Mine does it quite often, its as though it gets stuck. I get this without using any of the tools Gen....its a glitch in the viewport methinks.
Cheers bullet
bullet1968
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes