This was originally posted in August 2017 -- it's now March 2019 and I am having the same issue. Is there a fix? I discovered 47 people that need to be deleted from my tree. Since it's easier to do so on RootsMagic 7 for Mac, I deleted them there and planned to remove from Ancestry using Treeshare. The two trees are properly connected and RM ran the comparison and found the discrepancies. However, it will not permit me to reconcile them by removing them from the Ancestry tree via RM.
After the time it took for me to delete from RM, plus the time it took troubleshooting, now I have to delete from Ancestry manually. Such a waste of time. I tested it the other way around -- delete from Ancestry, run Treeshare, then delete from RM -- and it does not work either. Same error message. You can add people to either tree via Treeshare, but you cannot delete.
I tried to include a screen shot of the error message in this post but, of course, I got an error message on this site too ... LOL. Not my day I guess.