iMac: Unable to share video

Cannot share photo in Shared folder

I'm trying to use Shared folder on iMac to share a video between my wife's and my account but cannot click and drag the photo to the Shared folder. The action is forbidden. Any ideas how to do this? The video was taken on an iphone.

(I've also tried emailing the video to myself from my wife's account but I can't open the .mov file. in the email)

Thanks

Alan