That stinks, I almost had that happen to me just recently. When I was finally moved and settled I got a chance to look at my MTB after it had been sitting for a couple weeks, prior to regular snow duty over the winter. Poor chain had already started to rust, but after some attention with Simple Green and a toothbrush, then some ceramic lube it's back to normal. Amazing how all the squeaks went away!

In fact, I think I'm going to get that bike out on the trail tonight. Since buying my MTB I have been neglecting it something fierce.