I am using the excellent Validate plug-in, and I configured the submitHandler function to double check something with the user before submitting. When done, I was calling "form.submit()" and getting the error "form.submit() is not a function". I scratched my head over this for quite a while before stumbling on the answer (on this posting: http://www.spiration.co.uk/post/1232/Submit%20is%20not%20a%20function).
I had named the submit button "submit". As such, form.submit was the button, not the function. Upon renaming the submit button everything worked fine. It seems obvious now, but at the time I was only looking in the JS code for the problem, and wasn't looking at the HTML. I thought posting this might help someone else save some time... or just publicly prove how thick I can be at times.