Warnings when I add a sub category in my listings categories

Warning: array_keys() expects parameter 1 to be array, null given in /nfs/c11/h03/mnt/201747/domains/senta.lt/html/wp-includes/taxonomy.php on line 3901

Warning: implode() [function.implode]: Invalid arguments passed in /nfs/c11/h03/mnt/201747/domains/senta.lt/html/wp-includes/taxonomy.php on line 3901

Warning: Invalid argument supplied for foreach() in /nfs/c11/h03/mnt/201747/domains/senta.lt/html/wp-includes/taxonomy.php on line 3908

How do I fix this?