I am having the same problem. A few observations. Some vids (the older Logic 7 vids can't even be unchecked when I tried unchecking the Enable box as suggested but all the others can!
Hmmmm.
This tells me that NED is seeing these files differently. That is where one bug is! : ) You can see this in the first link below. Also notice that the server is called when I attempt to uncheck so the bug is likely somewhere near the code that calls the server. Maybe the server info that needs to be called has changed in relation to these older tutorials.
http://www.guitarpsycho.com/storage/macprovideobug/nedibug.jpg
Moving on....
If NED sees certain files as valid for disabling and others as not then I wondered what files do show up in our lists as available to sync? Maybe the differences that keep me from being able to disable a tutorial are the same ones that NED notices as not valid to put in the sync window.
Here are the only ones that work for me:
http://www.guitarpsycho.com/storage/macprovideobug/vidsinedi.jpg
It is interesting to note that one vid that shows up Steve's Masterclass could be unchecked in the first shot I provided. Note I have 2 Plugin tutorials because after Logic 8 came out I made the mistake of thinking a new one had been created. So one is older which explains why one could be unchecked (the newer one) and the other not (the older one)
I tend to think that the newer vids are more probable to show in the sync. And it might be related to this server checking that could be different between the two.
Forgive my verbose explanation and assumptions about something I know nothing about. : ) I just want this FIXED!!! : )