My grates became stuck today as well so I just let her burn. Figured it was a piece of coal. Tried again a few hours later and BINGO. All was well. When I went to dump the ash I noticed there a bottle cap in the ash. Burnt and bent. So I don't know if the grate was stuck because of the bottle cap or from a piece of coal. Doesn't look like the grates bent the cap but I feel lucky, very lucky that it fell through the grates.
I couldn't read the brand of soda or beer the cap was from. In case any one is interested the bottle cap came from a bag of Kimmels NUT.