cannot delete images from catalog

I don't think you can delete an image from disk when you're in a collection.

Right click the image and choose Go to folder in Library, then you can delete it.

You cannot easily delete images from the catalog when your current source is a collection. If you wish to delete images from the catalog there are two methods:

1. Have the folder that contains the target images, or All Photographs, as the active source then you can indeed delete from the catalog using the right-click menu.

2. If it's easier to work through collections to select images to be deleted, use the Reject flag (the X key on the keyboard) to mark the images as rejected as you find them. Then, when you've finished reviewing the collection(s), switch the source to All Photographs then use the option on the Photo menu>Delete Rejected Photos, which will remove all the images marked with that Reject flag from the catalog (or also delete them from disk).

There is a method to delete images directly from the catalog (and the hard drive) when the source is a collection, but I never recommend it as there is no confirmation warning when you use it, the images are simply instantly deleted from the catalog.