Are they very different?
Ok before submitting the form write down (or copy/paste to notepad) the value of the form's profilehash value (for this you would need to view the page source)
Then without leaving the form go and check the value of the profile hash in the database. It should be in the Users table, I think it is the last column, you'll see it anyway. Make a note of it and see if it matches the form's profilehash value. Then submit the form (and make a note of the values that script receives (you will need to add the modification again)
Post it here and we'll see what is going on. You can post it here safely I think because the hash changes everytime you load the form.