I tried to move a photo to my target collection. I get the error message . An internal error has occurred: ?:0:attempt to compare 2 nil values. How should I fix this? I have tried to optimismg the catalogue and doing a back up.
The task I tried before this error occurred was to import two photo into photoshop so that I could see them on one page, not sure if this is when the problem occurred as it is not something that I have tried to do before.
When you say "Import 2 photos into Photoshop" do you mean "Edit In" then select "Open as layers in Photoshop"?
That should not have any affect on placing image file names is a Target Collection. There is a bug in LrC V10 when using the b key to add images to the collection marked as the target collection. Whetehr that is the Quick Collection or some other one that you have marked as the Target Collection.
Try Selecting the images and Click + Drag to the collection you want them in.