Help please, Calibre and Kindle. 2 kindles

I hope I am in the right place. I have two kindles at home and the one I use for myself and have bought these books on will not recognize the books if I send them from Calibre. "This item cannot be opened because it is licensed to a different user. Delete the item and download it from your Archived items or purchase a copy from the kindle store." This occurs whether I have changed the book metadata or not. I cannot find anything here or anywhere else that can help me with this problem. Is there something in the calibre program that will let you differentiate between to different kindles? Mind you I don't think that will change my problem but I don't know what the problem is. If the books are sent to kindle pc then calibre has access to them thou drm will not allow them to be read with the calibre, but it still should let me read them on my kindle if I use calibre to download them on my kindle!!!
Please please someone put me out of my misery and help.
thanks Paula:blink: