MySQL - Questa versione di MySQL non supporta ancora la sottoquery "LIMIT &IN/ALL/ANY/SOME

Invece di usare IN, puoi usare JOIN

SELECT v.VID, v.thumb
FROM video AS v
INNER JOIN
     (SELECT VID
     FROM video
     WHERE title LIKE "%'.$Channel['name'].'%"
     ORDER BY viewtime DESC
     LIMIT 5) as v2
  ON v.VID = v2.VID
ORDER BY RAND()
LIMIT 1