I'm not sure whether it's 1.5 or a combination of both, but after several hours of debugging, I've discovered that this following commit is crashing my server at startup:
#256 (Feb 25, 2013 11:19:28 PM)

make sure aync call does not look for the sign in the world

Here is the relevant part of the stack trace: http://pastie.org/6647724
Here is the entire log: http://pastie.org/private/amey8xfyajntr7emkmubhq

This is exactly what is being shown in console when it crashes:
http://pastie.org/private/bdii2lfgh3iqgbhzotjl2q

I narrowed it down to that commit because literally just reverting that commit allows me to start my server fine. I'm not sure what the implications are for reverting that code.

I hope the solution is simple, thank you for your time!

let me know if that did it, thx

So far so good. Server is loading without crashes, I'll let you know if any [Rent] async issues come up, thanks!