I had a customer question the other day that I hadn't seen before. The issue was that people were noticing that every time when they initiated an IM conversation to a specific user, they would get the following in the IM window:
Context not supported: this conversation includes context which requires a Microsoft Lync plug-in. Please contact your administrator to enable this context.
What was interesting is that it only happens in one direction. Using the users in the example above, anyone initiating an IM to Judith saw the issue, but if Judith initiated the conversation, the message wasn't displayed in either IM window. We looked at the trace file from William's Lync client and it shows an INVITE being received by the Lync client with information about an application ID:
It turns out that Judith has a Conversation Window Extension (CWE) registered on her machine. You can learn more about contextual Lync conversations and Conversation Window Extensions here. This application was only registered on Judith's local machine and not everyone else that was trying to IM her. If other users had the same application installed, they wouldn't see the message in the IM window. To figure out what the application was we opened Registry Editor on Judith's computer and navigated to:
This shows that the name of the application is "Logi Far End Control":
Looking in Programs and Features shows that Judith installed a plugin from Logitech. Specifically this plugin is used for far-end camera control for a Logitech webcam:
The user didn't need the far-end camera control plugin installed, so after they uninstalled it users were no longer getting the message in their IM window.