what i found is, if u uncheck iCloud contacts under internet account, then it work fine, i can then forward a website using the share menu in safari or file using the share menu in the contextual menu(right click)
All others do work as example if you want to forward a website or a file to someone by email that works but with iMessage nothing happens.
I'm using Sierra on a iMac.
I created a new user using the same icloud account and apple id and it works fine, the small iMessage windows shows up when i try to forward either a file or webpage. I have deleted the new user following this since it was just to test if my user profile was damaged or something.
So still looking to resolve this issue in my original user profile
Best Answer
I am using sierra as well I did what was suggest here:
I unchecked the contacts on icloud settings and then tried the share via imessage and it worked. Then I checked back on the contacts on icloud contacts and it worked again
I did this from safari, when I tried from a file folder it did not, so I went back to uncheck the contacts on icloud and repeated the sequence described above and it worked
It seems to me that from each place you want to share something via imessage you have to turn off contacts, try it, turn it back on again and this seems to correct whatever it is that was wrong
But after a little while it stops working again if you have contacts activate in icloud
I guess the next step is to try to loggoff from the icloud account and re login to see if this gets fixed