Did you maybe grease the cookie sheet when it was supposed to be ungreased? Sounds like a problem with the shortening to me...but I'm definitely not an expert. This happened to me a couple months ago and it was just a problem with me greasing the cookie sheet when I wasn't supposed to...I think...still kinda early and my brain's not working yet...LoL. I'll remember after I click submit.
a couple of possibilities...
1. not enough flour
2. dough too warm when you put it in the oven (or the cookie sheet was hot)
I always freze my cookie dough for 10-20 minutes before baking 'cause i like thick chewy choco chip cookies... it's also great for cut-out cookies as they hold their shape better!
Did you use butter or margarine, and if so was it at room temp or was it melted? I read somewhere, I think on Baking911.com actually, that if the butter is too soft, the cookies will spread more when baking. If that's not the case, then I'd say it was due to there not being enough flour in the batter...
Alton Brown did a chocolate chip cookie show once. He demonstrated that if you use butter/margarine the cookies spread and are thin. If you use crisco/buttter flavored crisco - they are thick and chewy. I have found a happy medium - I use 1/2 butter and 1/2 crisco~ Makes a nice chewy (not thin) cookie.
My non-baking girlfriend took my oatmeal choc chip recipe and called me almost in tears. Her cookies had spread until she had one big gooey mess. I lovingly said, "Miss Betty Crocker, tell me exactly how you made them." It took three phone calls before I got the whole story. She melted the butter instead of softening it and she was 1 cup short on the oatmeal. Duh!
I wouldn't freeze my cookie sheets before putting them in the oven. You might warp them. Not having enough flour was probably your problem. I think the brand of choc chips sometimes affects the outcome also. Cheaper ones don't do as well sometimes.
Diane
I freeze mine all the time... no problems! You don't leave them for days... just 10-15 minutes.
As for the butter vs margarine vs shortening... margarine will definately give you cookies that spread more as it contains more water that butter or shortening. Unless your recipes specifically says butter or margarine, stick to butter (and margarine does not mean the soft spread stuff... it has even MORE water in it!
Whenever I make choco chip cookies, I always double the recipe and freeze the extra dough... just roll it into a sausage shape (diameter about the same as you'd want a cookie) in a sheet of waxed paper... twist the ends and pop it in the freezer! Then I can make just a couple of cookies... I just cut off (with a sharp, hot knife) individual cookie amounts... plop them on a cookie sheet, and bake 'em up!
BTW... if you're making a big batch of cookies and re-using your cookie sheets, make sure they are cooled before adding the next batch of dough or you'll have the same spread problems.
Too much spread sometimes has to to do with your baking temperature. Consider what the melting point of butter is. If you used butter in your recipe but didn't bake it at the right temperature this may be why. Often times when I roll out my dough, I use powdered sugar. It absorbs moisture and does not add more flour to the point of toughening your cookie. Also, I often replace butter with shortening in a cookie recipe because there will always be less spread, which is due to the melting point. Just a thought.
MelC, if I made extra dough and put it in the freezer, I would have it eaten raw before I ever got around to baking it! 
My weakness!
I use 4 sheets when making cookies. One in the oven, One with cooling cookies on it, one cooling completely off (with nothing on it) and one that I have ready to go into the oven (already cooled with the dough on it) I have a rythum down and it goes very quickly that way. the cooled off one gets washed before the next batch goes on too - unless I am using parchment paper that day.
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