We have the following random error on one of our Tridion 2013 server (SP1 HR1) when using the Experience Manager :
Could not connect to net.tcp://localhost:2660/CoreService/2013/netTcp. The connection attempt lasted for a time span of 00:00:02.0313468. TCP error code 10061: No connection could be made because the target machine actively refused it [::1]:2660.
It appears often (but not always) when we try to Insert Content > Create and insert new Content. The server is loading a long time then finally the list of sample components is displayed but when we click nothing happens and a lot of error messages (like the one above) are returned.
Update 1 : when activating perfmon on the Content Manager server, I can see that when we click on the button "Create and insert new content" there is a high number of active requests that are made to the Core Service. When I say high, it seems that we bypass the number of authorized active connections (more than 200) and finally the IIS drop them. And we have the "could not connect" error. Now the question is why do we have such a number of calls to the Core Service ...