Exception [ 0 ]: @todo UNABLE_TO_LOCK_EXCEPTION

I made the mistake of organizing 2 albums at the same time and a directory in my temp directory was deleted but still showing in the album.

Now when attempting to delete the album, I get the following error/exception:

Exception [ 0 ]:
@todo UNABLE_TO_LOCK_EXCEPTION
MODPATH/gallery/libraries/ORM_MPTT.php[ 331 ]

326 */
327 protected function lock() {
328 $timeout = module::get_var("gallery", "lock_timeout", 1);
329 $result = $this->db->query("SELECT GET_LOCK('{$this->table_name}', $timeout) AS l")->current();
330 if (empty($result->l)) {
331 throw new Exception("@todo UNABLE_TO_LOCK_EXCEPTION");
332 }
333 }
334
335 /**
336 * Unlock the tree.
MODPATH/gallery/libraries/ORM_MPTT.php[ 102 ] » ORM_MPTT_Core->lock()
MODPATH/gallery/models/item.php[ 98 ] » ORM_MPTT_Core->delete()
MODPATH/gallery/libraries/ORM_MPTT.php[ 96 ] » Item_Model_Core->delete()
MODPATH/gallery/models/item.php[ 98 ] » ORM_MPTT_Core->delete()
MODPATH/gallery/controllers/quick.php[ 104 ] » Item_Model_Core->delete()
{PHP internal call} » Quick_Controller->delete( arguments )
SYSPATH/core/Kohana.php[ 331 ] » ReflectionMethod->invokeArgs( arguments )
{PHP internal call} » Kohana_Core::instance( arguments )
SYSPATH/core/Event.php[ 208 ] » call_user_func_array( arguments )
APPPATH/Bootstrap.php[ 67 ] » Event_Core::run( arguments )
DOCROOT/index.php[ 116 ] » require( arguments )
Environment

Any ideas how to correct this?