Sir, I would suggest to wait a day or 2 untill SM comes with a solution for your particular installation.

Yes, with a default installation, uninstalling the previous SR would work.

But having no details of your particular install and given the fact that SR2.1 did not install as expected on your system/installation, my best proposition would be to wait a little bit. SM might ask extra questions to troubleshoot.
The team will surely come with a solution.

But give SM the time to come up with a solution, or you might run in the same situation for future SR's..

What WILL work is a complete uninstall.
Install the origional 16510 and then run the SR2.1.

As ever;

I STRONGLY suggest a default install in Program files, and the Content runtime in the shared folder. (as proposed by the initial installation.)

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!