( 27 :: 38 ) Cannot Insert an item into a locked list

[Sebastian Ballek]

Hi Folks

After Effects Error: Cannot Insert an item into a locked list. (27 :: 38)
Anyone know what this error is? I get that when I try to duplicate my footage, or copy footage from one comp into my main comp.

When I erase the last layer I was working in the problem disapears and I can copy layers in the comp again. It did happend with two diferent layers I worked in and had to erase.

This is how the proyect looks like:
https://img218.imageshack.us/my.php?image=aeerrorpx2.jpg