I experienced a very similar set of symptoms this morning—after riding my bike in the rain on Friday, I parked it outside and left it there for thew weekend (which included clouds, sun and rain). It was mostly dry, with just a bit of night-time moisture left on it this morning. I fired it up and had gotten just about far enough to think "damn, this is a nice day for a moto ride" when the bike cut died suddenly. Side-of-road troubleshooting eventually revealed intermittent clicking noise from one of the injectors, as if it were firing constantly once the key was set to "on" (but not every time I tried to fire up the bike). No low fuel light, which I think suggests that fuel pressure is okay, and at least when I started troubleshooting, voltage was fine (dropped to 12V over the course of repeated attempts to start the bike).
Having the bike in neutral doesn't seem to affect matters, which should rule out the safety switches.
I ordered a new HES from Beemer Boneyard; it may be a pricey step without being 100% sure of the problem, but given my current free-time quota, I think it's worth a shot.
(My bike is a 2000 R1150GS with about 103k on it, BTW)