As we already know, you can't put one formPanel inside another - therefore you probably have two options:
1.) Think of a way to alter your layout so these two sections can co-exist inside their own separate forms.
2.) Manually handle all the formfields within your "tabpanel1" and submit these via an AJAX call instead of a form submit (i.e. give all your fields IDs or loop through the panel's items object, grab the input values one by one, then submit these as your AJAX params).