Results table with form select for filtering
I don't see a render function anywhere after you create the form. If you didn't exclude it on purpose, after creating the form, it has to be rendered and printed.

in your function you call drupal_get_form()


  Return value
  
  The form array.


and later on you add to that with theme()


  Return value
  
  An HTML string representing the themed output.


it looks like you're trying to put together an array and string in the same variable. You need to either render the form first into a string and then add them together, or include the theme data into the form array and render it later on.