Do you have access to the Windows server?
First I would check the Spool Directory for the Application.Generation directory and look at the job output if any. What is in the file?
Next open a Windows Command prompt and navigate to the Log directory and enter the following command.
findstr "device not ready" *.log
Does the command above find anything?
I would expect there is at least an entry in the transmitter.log
If it does open that log and review all messages, there may be something of meaning before or after the message.
If you have not already created an ESP Test PROC to verify agent functionality I would recommend you do that. If you need help setting that up let me know.
I am not a fan of starting/stopping the agent or the server to "fix" problems, since all that does is mask an issue.
Define the problem and work on a resolution.
You can also open a Priority 4 "Question About Use" case we CA and see what they say.