Rollback net framework 4.6.1 to 4.5.2

1. If the server has already automatically updated to 4.6.1 and has not rebooted yet, do so now to allow the installation to complete
2. Stop all running services related to Exchange.  You can run the following cmdlet from Exchange Management Shell to accomplish this:  (Test-ServiceHealth).ServicesRunning | %{Stop-Service $_ -Force}
3. Go to add/remove programs, select view installed updates, and find the entry for KB3102467.  Uninstall the update.  Reboot when prompted.
4. Check the version of the .NET Framework and verify that it is showing 4.5.2.  If it shows a version prior to 4.5.2 go to windows update, check for updates, and install .NET 4.5.2 via the KB2934520 update.  Do NOT select 4.6.1/KB3102467.  Reboot when prompted.  If it shows 4.5.2 proceed to step 5.
5. Stop services using the command from step 2.  Run a repair of .NET 4.5.2 by downloading the offline installer, running setup, and choosing the repair option.  Reboot when setup is complete.
6. Apply the February security updates for .NET 4.5.2 by going to Windows update, checking for updates, and installing KB3122654 and KB3127226.  Do NOT select KB3102467.  Reboot after installation.
7. After reboot verify that the .NET Framework version is 4.5.2 and that security updates KB3122654 and KB3127226 are installed.
8. Follow the steps here to block future automatic installations of .NET 4.6.1.

source:http://blogs.technet.com/b/exchange/archive/2016/02/10/on-net-framework-4-6-1-and-exchange-compatibility.aspx