Sorry you're having trouble. We've heard of intermittent issues where XD thinks you're not signed in even though you are. Could you try the following steps and see if they fix the problem for you?
1. Quit XD
2. In the Creative Cloud desktop app, click the gear icon in the upper right and choose "Preferences..."
3. Click the "Sign Out" button
4. After signing out, sign in again
5. Restart XD and try to share again
Please let us know whether this clears up the problem for you. Thanks!
this fixed my issue - much appreciated
Great, thanks for letting us know!