Hello,
after updating node.js version from 0.10 to 0.12.4, PM2 started to give me the issue described above.
If I launch an app with the cluster mode, the first cluster will remain stuck on the launching status and it won't work.

Hmm can you kill everything pkill -9 PM2; pkill -9 node;, install PM2 v0.14.1 (latest) and try again ? :)
Thank you @jshkurti :) solved! I've got 0.14.0 version, once updated it worked!
I have the same issue with pm2 1.0.0...
Edit: I killed all processes related to node and started pm2 again. It worked then.
I have the same issue on PM2 version 1.1.3
I've tried to kill all PM2 & node processes and still not working.
Most helpful comment
Hmm can you kill everything
pkill -9 PM2; pkill -9 node;, install PM2 v0.14.1 (latest) and try again ? :)