"ONLINE_USER_COUNT_SETTING is immutable" error if you manage user roles by SDK in Skype for Business Server 2015

Symptoms

Consider the following scenario:

• You are a developer in a Microsoft Skype for Business Server 2015 environment.

• You use Persistent Chat Software Development Kit (SDK) to manage user roles in a chat room by invoking BeginAddUsersOrGroupsToRole method.

In this scenario, the method call may fail, and you receive the following error message:

Cause

This issue occurs because room search command tries to set a parameter value that's an external read-only field.

Resolution

To fix this issue, install the December 2017 cumulative update 6.0.9319.510 for Skype for Business Server 2015, Persistent Chat Server.