Won't delete selected files

I am having several odd problems, the most recent being that it fails to delete selected files. The attached screen capture shows a few selected files (in fact there are over 3000 - I'm cleaning out an old disk) and below the selections I have made. I have selected the top level folders which have about a dozen folders below the top level. Yet when I click on Delete, the confirm delete box appears, I click on Delete, the box disappears but no files are deleted.
If on the other hand I try just selecting a sub-folder rather than the top level folder, it works fine.
I am using Windows 7 Pro 64bit.

If you right-click one of the files and choose Delete, does that work?

If not, what happens if you try to delete the same file using Explorer?

Some of the files appear to be locked though I am not sure why. permissions are for Read/Write

I've just tried again and same problem. The delete button won't delete any files but I can delete files right clicking individual ones.

Note that if you want to delete files found through the Duplicate Files finder you have to use the Delete button in the actual Duplicates panel (at the bottom) - the regular delete button on the toolbar won't work.

Thanks but that is the one I am using.

If you turn off Preferences / File Operations / Deleting Files / Delete to Recycle Bin where possible (supports undo) does it work then?

Will check that out later - work calls! However there is another problem which may or may not be related. If I search for duplicates between two folders which only have a relatively small number of sub-folders and files, then selection & deletion works OK with duplicates being flagged for deletion. However if I select two large capacity folders then while duplicates are identified, they are not marked for deletion. The drive I am clearing has 195Gbytes of free space but the one which I am keeping has 30.9Gbytes.
Any bearing on the case?

Amount of free space on the drives should make absolutely no difference.