motion blur doesn't turn on
 

It seems that whenever I'm working on a large scene or dealing with a lot of particles I can't turn on my motion bur on my render settings. I click on the motion blur box but the checkmark doesn't appear and nothing happens. I looked in the script editor and it says that motionblur is locked or connected and cannot be modified. any ideas on how to "unlock it"?

an alternate solution would be importing the whole scene on a new project that already has motion blur turned on but then I get other importing problems with shaders and plugins that are making my problems worst.

but anyways, thanks for any help,
Dan

haha its 2am but I finally got it. sorry for the post I'd delete it if i could. But heres what you gotta execute:

setAttr "defaultRenderGlobals.motionBlur" -l 0;

I don't know what the -l means but that was the key. cgtalk says they get that attribute to lock all the time but don't know why.
thanks anywyas fellows