What happened exactly?
Did GIFWorks allow you to load and open the file?
If it did, how did you try and reduce the file size? by reducing the physical dimensions or by reducing the colour palette? or something else?
If you want to post the file up here I'll have a play if you like.
I don't have any gifs on my machine of that size..
I'm no expert on using it but have just used it to reduce down some avatar type sized animated gifs so that they were a bit smaller....