pgAgent not working on linux (Ubuntu 14.04)
Late answer but...


  What is causing the above messages and what needs to be done to get pgAgent to run scheduled tasks?


Seems that, as stated in comments, this boils down to why the .pgpass file is being ignored. 

Reading the documentation I found the following relevant details on this page, emphasis mine:


  On Unix systems, the permissions on a password file must disallow any access to world or group; achieve this by a command such as chmod 0600 ~/.pgpass. If the permissions are less strict than this, the file will be ignored. On Microsoft Windows, it is assumed that the file is stored in a directory that is secure, so no special permissions check is made.


So, if your .pgpass file does not have such permissions it will be ignored. This could be what is causing the error you see.