Just in case any of you has a large file numbers in a scene that you'd like to check the mode "No OSL" on, just run this script in a python shell.
If you would like to activate the No OSL mode on all files, just replace the 0 by a 1 in the script.
import maya.cmds as cmds
files = cmds.ls(type='file')
for i in files:
cmds.setAttr('%s.mtco_noOSL'%i, 0)