I have http://www.pbxfreeware.org/app_contest.c installed;

I get the following error in the CLI:
    -- Executing contest("SIP/66.54.140.46-40413340", "") in new stack
Aug 15 11:46:08 NOTICE[23827]: /usr/src/asterisk/apps/app_contest.c:60 contest_exec: Caller 1
    -- Playing 'invalid' (language 'en')
  == Spawn extension (cell, 7, 1) exited non-zero on 'SIP/66.54.140.46-40413340'