Problems setting up RTC Development Server in RTC 6.x Extensibility Workshop

I'm trying to work through the 6.x Extensibility workshop with v6.0.4 RTC but when I try to run the server.startup script, I get the following output:

Listening for transport dt_socket at address: 3388
Starting server clm.
Server clm start failed. Check server logs for details.

Inside the console.log file I get this:

ERROR: [Agent.cpp:186] JDWP error in VM_INIT: TransportException [510/201] binding to port failed (error code: -213)