Why can I not edit object texture nodes? I was working on a model, and I wanted to edit some texture nodes. So I went to the node editor and switched to the texture tab, but there was no way for me to select the the texture:



But when I switched to world texture, I was able to select a texture again.



The problem wasn't solved after restarting blender. So I wanted to see what would happen if I loaded another file or created a new one. After doing this, I was able to edit object texture nodes:



As you can see, only one blend file is being affected. Does anybody know what would be causing this or how it could be fixed?
The object texture list shown in the node editor is generated from textures used by Blender Internal render engine materials. A material and one of it's textures needs to be selected for this list to show up even though every available texture will then be listed.

These texture slots are only accessible when the Blender Internal render engine is active.

This means that the texture slots need to be created while Blender Render is active, if Cycles is chosen after the slots are populated then the list will still be visible in Cycles, though they will have no use for the material. Materials created while Cycles is active will not have any material slots and will not show the list in the node editor.