I hope that name of your config for nxagentd(NX agent) is "nxagentd.conf", not "netxmsa.conf". What does agent writes if you start it from console like: "C:\ProgramData\NetXMS\bin\nxagentd -D6"
Config file for the server should be named "netxmsd.conf" and for the agent "nxagentd.conf"
Config file for the server should be named "netxmsd.conf" and for the agent "nxagentd.conf"