Share screen not working - i get an alert that i can't share screen all the time.

A Screen sharing alert (cannot share screen) appears whenever i join or someone joins me on a Zoom session. I can't share screen, it's been going on for a few weeks already. 

I tried logging out and then logging in,  downloading updated client, unistalling Zoom and re-installing it. 

Checked all security definitions.

Happens on sessions i start, or sessions i'm invited to.

What can be the problem??