As you can read here, the installation of the RTM version of NAV 2016 overwrites the NAV 2015 Administration Tool.

With the first Cumulative Update, this has been fixed. The NAV 2016 Administration Tool now got its own registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MMC\SnapIns\FX:{BA484C42-ED9A-4bc1-925F-23E64E686FCF}

Only the last character was changed from E to F.

If you never installed NAV 2016, I recommend to skip RTM and go directly with CU1. But if you have installed RTM before, there can be different situations after installation of NAV 2016 CU1. Depending on the installation method and whether you applied the fix or not, you may need to perform some extra steps. I try to explain the different situations and how to solve them.

Choose your CU1 installation method:

Uninstall / install with setup.exe

Uninstalling NAV 2016 RTM version and installing CU1 will remove the original registry key and install the new one. Look at ‘Choose your situation’ below to check if you need to repair NAV 2015.

PowerShell update script

If you use the Copy-UpdateFilesToBatchDirectory.ps1 to install CU1 you will not get the updated registry entry. Hence, the NAV 2016 Administration Tool will not load after you used the PowerShell script to update to CU1. This can be fixed by following these steps:

1. Download the correct NAV2016 CU1 registry file here.
2. Extract the .reg file and import it by double-clicking it.

This will delete the original NAV 2016 registry entry and add the NAV 2016 CU1 registry entry. In other words: it gives exactly the same result as using the uninstall / install method.

Choose your situation:

No fix applied for NAV 2015

In case you did not apply the fix from my previous post, the uninstall / install method or the steps above for the PowerShell update script will not bring back the Administration Tool for NAV 2015. To repair this, you can follow these steps:

1. Download the original NAV 2015 registry file here.
2. Extract the .reg file and import it by double-clicking it.

Applied the fix for NAV 2015

If you did apply the fix, both NAV 2015 and NAV 2016 Administration Tool should work after uninstall / install or by following the steps for the PowerShell update script. Only in case you want to revert back to the original NAV 2015 installation (because you prefer to have a clean environment), please follow these steps:

1. Download the original NAV 2015 registry file here. Extract the .reg file and import it by double-clicking it. This will also remove the registry entry that was created by the fix.
2. Copy the original file Microsoft Dynamics NAV Server.msc from the NAV 2015 DVD folder \RoleTailoredClient\program files\Microsoft Dynamics NAV\80\RoleTailored Client\ to the NAV 2015 Client installation folder: C:\Program Files (x86)\Microsoft Dynamics NAV\80\RoleTailored Client\