This issue has already been reported and it’s also been addressed. I would like to post this still. To act more like a pointer. It’s quite crucial in nature.
I have been testing GP2015 R2 upgrade on my test environment when I faced the following error message:
Quite evidently, upgrade didn’t go through after. I remembered this being posted on our GP Support & Services blog. Dug the post and got the solution.
Here’s the post: Known Upgrade Issues When Upgrading To Microsoft Dynamics GP 2015 R2
Please note that this has been fixed already and is available with June 2015 Update.