When loading the ee upload library in the publish form mapper, configure the upload path using the following syntax: ee()->load->library('filemanager', array('upload_path' => dirname($destination->server_path)));
Depending on the original path, dirname() may not be the correct choice here, since it chops off the last path segment. Check that filemanager and upload libraries are configured consistently.
When loading the ee upload library in the publish form mapper, configure the upload path using the following syntax:
ee()->load->library('filemanager', array('upload_path' => dirname($destination->server_path)));