couple of questions here ?
Have you completed with agent trouble shooting as mentioned here RSCD Agent Troubleshooting - BMC Server Automation 8.5 - BMC Documentation
Does your appserver is configured to use process spawner. If yes, then verify below things.
-Process Spawner is running.
-The Application Server is configured to use the correct port the Process Spawner is listening on or vice versa (check blasadmin settings to verify)
-If any ports are blocked between the Application Server and Process Spawner services.
Correcting one of these scenarios should address the issue.