It means what it says: There is no file included in the current page request that contains the definition for a function called
A quick Google search shows that this function is part of the
ModalFrame API module, for which there is only a Drupal 6 release (not Drupal 7). I guess you've copied this code from a Drupal 6 site without changing it?
The comments on the ModalFrame API module page say:
It seems this feature is being included in Drupal core itself. So, probably there will be no stable release of this module for Drupal 7 because it will be already there
My best guess is that the Drupal 7 equivalent of this function is
overlay_close_dialog(), but I can't comment as to whether that will work as in a drop-in replacement for you current code.
It might be worth reading the Initial D7UX admin overlay thread, it's basically the discussion about moving ModalFrame API into core.