Check the c2o.log file located in the PAM install directory under server\c2o\log. Search for the word ERROR in capital letters. It will begin the line of any error messages that should be reviewed.
It could be many things, but the first thing that came to mind is that perhaps something has locked the port that PAM needs to use. You will see this reported in the logs as "already in use" and it should give the port number that is in use and needs to be freed.