We observe the following behavior when the Introscope Enterprise Manager (MOM) has this problem:
Not allowing any workstation client to connect to Introscope Enterprise Manager MOM.
Not allowing any Webstart to connect to Introscope Enterprise Manager MOM.
Not allowing any Webview to connect to Introscope Enterprise Manager MOM.
However, we can connect to Introscope Enterprise Manager (collectors) successfully.
We also see following error in the IntroscopeEnterpriseManager.log around the time this problem occurs:
[ERROR] [Dispatcher 1] [Manager.Dispatcher] Dispatcher 1 Unexpected exception java.nio.channels.CancelledKeyException
Issue with NIO implementation in Enterprise Manager, there is no negative impact to disabling this property
Enterprise Manager 9.1 cluster, particularly prior to 9.1.5 but similar behaviour can be seen in even more recent releases, just without the particular error
Disabling NIO can still be a useful option if you are seeing problems with Workstation / WebView connection in more recent releases.