Consider the following scenario:
You install an English version of Microsoft Skype for Business Server 2015 on a Turkish version of Microsoft Windows Operating System.
A user parks a call by using a Skype for Business client or a Skype for Business-enabled telephone.
The client or telephone is connected to your Skype for Business Server 2015 server.
In this scenario, any user cannot unpark the call.
Note This issue will also occur when the parked call has timed out.
To resolve this issue, install the June 2015 cumulative update 6.0.9319.55 for Skype for Business Server 2015 and Unified Communications Managed API 5.0 Runtime.