Lync 2010 requires additional software to sign into Skype for Business Online

Problem

When you try to sign in to Skype for Business Online (formerly Lync Online) by using Lync 2010, you receive the following message:

To sign in, additional software is required.

When you click Download and install now?, you're prompted to download and install the Microsoft Online Services Sign-In Assistant.

Screenshot that shows the Lync sign in page, including error message Download and install now? link.

Solution

Make sure that Microsoft Online Services Sign-in Assistant is running on Windows Services by following these steps:
(These steps are for Windows 10)

  1. Right-click the Start button and select Run.
  2. Type services.msc and select OK.
  3. In the Services window, check whether the Status of Microsoft Online Services Sign-in Assistant is listed as Running.

More Information

This issue occurs if you try to sign in to Skype for Business Online by using Lync 2010 on an operating system that doesn't have the Microsoft Online Services Sign-In Assistant.

Still need help? Go to Microsoft Community.