Robert Reich's Blog: The Meltdown (Part IV): 
"Why? Because the underlying problem isn't a liquidity problem. As I've noted elsewhere, the problem is that lenders and investors don't trust they'll get their money back because no one trusts that the numbers that purport to value securities are anything but wishful thinking. The trouble, in a nutshell, is that the financial entrepreneurship of recent years -- the derivatives, credit default swaps, collateralized debt instruments, and so on -- has undermined all notion of true value."