Local Configuration Store can't be installed when disabling TLS 1.0/1.1 in Skype for Business Server 2015

When you install the Local Configuration Store by using the Microsoft Skype for Business Server 2015 deployment wizard, the installation fails, and you receive the following error message:

Prerequisite installation failed: Prerequisite installation failed: SqlInstanceRtcLocal For more information, check your SQL Server log files. Log files are in the folder C:\Program Files\Microsoft SQL Server\MSSQL*.RtcLocal\MSSQL\Log, where the * represents your SQL Server version number. For example, SQL Server 2012 uses this path: C:\Program Files\Microsoft SQL Server\MSSQL11.RtcLocal\MSSQL\Log.

In addition, an Event ID 26011 could be logged in the Event Viewer. This issue occurs when you enable the TLS 1.2 and disable the TLS 1.0/1.1 on the operating system.

This issue occurs because the setup installs a version of SQL Express that does not support TLS 1.2.

You have to enable TLS 1.0 and TLS 1.1 on the local computer; uninstall Microsoft SQL Server 2014 (64-bit) through Programs and Features in Control Panel, and then rerun step 1 - Install Local Configuration Store and step 2 - Setup or Remove Skype for Business Server Components. After that, update SQL Server to the version that supports TLS 1.2, and then disable TLS 1.0 and TLS 1.1 again after SQL Server is updated.

To fix this issue, you have to select the Connect to the internet to check for updates option to install the latest cumulative updates before the installation of Skype for Business Server 2015. This makes sure the SQL Express server that supports TLS 1.2 will be used.