perhaps i'm not explaining very well
in dreamweaver if i look at my files panel I can see all my files listed. if i select 'assets' panel & highlight one of the problem images I dont get a preview (just this generic icon in preview pane). if i select another good image I see the preview.
i'v handled these much the same as all images & examined them & all appear ok - but cannot drag into my page in the usual way.
hope that clearer!!!