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:
NodeSetting.ONLINE_USER_COUNT_SETTING is immutable
This issue occurs because room search command tries to set a parameter value that's an external read-only field.
To fix this issue, install the December 2017 cumulative update 6.0.9319.510 for Skype for Business Server 2015, Persistent Chat Server.