The error message that you've mentioned is entirely harmless. Centova Cast keeps track of Shoutcast's PID itself and does not need Shoutcast's PID file.
Unfortunately there is no option to change the path to dnas2's pid file nor turn it off. Shoutcast always wants to create it in whatever directory it started up in (in this case /usr/local/centovacast/shoutcast2), and that directory is not writable, thus the error.