When starting a second StreamBase fragment launch from Studio during development, the following error occurs:

status (node install): A.myuser- TRACE: epadmin.exe install node nodedirectory=C:\Users\myuser\Documents
  \StreamBase Studio 10.1 Workspace nodename=A.myuserbuildtype=PRODUCTION javahome=C:\TIBCO\sb-cep\10.1\jdk 
status (node install): A.myuser- Installing node 
error (node install): - install of node A.myuserusing discovery port 54321 failed: the service name is already 
  in use by service address othersystem:port
failed (node install): returnCode = -1

The launch then fails.
 

Each new application in the same subnet needs a unique node.cluster identifier.

The node.cluster identifier used by StreamBase Studio by default is node="A", cluster="username". Since the same user started both applications under the same node-name, this collision occurred.

Change the node.cluster ID for each workspace using menu: Window > Preferences > StreamBase Studio > Cluster, and change either or both of "Cluster name" and "Nodes".

When a StreamBase Runtime application is launched, at the same time a discovery service is started (default port 54321) using UDP to respond to multicast requests so the new node can join the named cluster. Within the cluster a node must have a unique name. If the node is not intended to join a cluster, the cluster should have a unique name on the subnet.

To see what nodes are visible to you on the LAN, run:
   epadmin display services
for any instance you own that shouldn't be running, use:
   epadmin servicename=node.cluster stop node
   epadmin servicename=node.cluster remove node

To run the epadmin command you will have had to complete the shell environment setup described in the documentation under topic:
  TIBCO StreamBase Documentation > Installation Guide > Configuring Shells for StreamBase