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Why didn't you use parchment paper?

Here are a bunch of "maybes:"

1) Oven not calibrated. Use a digital probe thermometer hung on one of the racks. Preheat the oven. Set the temp alarm for 350. When the temp alarm goes off, watch the digital readout to see if it goes above 350, then note where it stops. It could be as high as 400 or 425 which would cause burning.

2) In a regular oven (non-convection), the racks should be set at the upper and lower thirds of the oven. If you have a rack set just over the element, this would cause burning.

Did you notice if the pan was burned from end to end or only one side? If your element is not heating correctly, it cold be spewing flame or heat from only one side. This would cause the tray to burn because it's working 2x as hard to heat the oven but it's only happening on one side. Just a thought.

I think it's more than just greasing, non-greasing or parchment. There is a serious temperature disparity between where you're setting your oven and where it's going.

PS - Since I discovered parchment paper, I have NEVER greased a cooky sheet. I also re-use the parchment for multiple batches. Silpats are nice but expensive. Get some parchment from a restaurant supply store where the sheets are stored flat and not in those annoying rolls. You'll never grease another cooky sheet again.

I would have to agree about checking your oven calibration.

Also are you baking more than one sheet of cookies at a time? If so, are you rotating the sheets front to back, top to bottom, halfway through baking? I've found it's really best to do one sheet at a time. If only using one pan at a time, what rack are you baking on, you may need to move it up.

chiff makes excellent points, and please seek out some parchment paper or Silpat's they'll be your best friends. I buy the rolls (because they are easy to find) and cut sheets the size of my baking sheets and store the parchment between 2 baking sheets to keep them flat. I also use restaurant supply store purchased Lincoln Wearever baking sheets and don't bother with cookie sheets unless I need a pan with no edges.

I've also found that when the outside of the cookies are brown, your cookies are done, they will be soft in the middle, but still bake a few minutes out of the oven, so unless you like them super crispy, keep a close eye on them.

Hope you have more luck with your new batches.

Another vote for half sheet pans + parchment paper.
You might be having problems with your oven - do you have an oven thermometer?

chiff: i never thought of getting the parchment from a restaurant supplier so it'll be flat-genius!

imagine that-& here i thought i wouldn't learn anything new from this thread. :)

Yet another vote for parchment paper. I buy mine in bulk and was just telling OH the other day that I don't know how I'd go through all this baking without it. I even use it to form logs of cookie dough and deal with other similar sticky situations, whether it's pressing granola bars or forming logs for biscotti - I keep my hands clean and the dough or whatever stick stuff I work with stays together.

And by all means, check the temperature of your oven, like chiff and Jerzee have advised.

Half-sheet pans yes, but I disagree about parchment in some cases. When you have baked goods that are meant to rise a LOT (some cookies, biscuits, scones), parchment cuts down on their resistance against the bottom of the pan and can decrease rise. I usually grease my pans unless the cookie is extremely delicate, and I never have problems.

Another vote for parchment. Also, try rotating the trays halfway through baking. If they look like their cooking too fast, Pull them and let the cookies sit in the trays for a minute or two. There will be carry-over cooking time.