I found a support case that has a solution to your problem. The problem was seen in environment where agent host memory for overloaded.
I'm pasting in the support engineer's recommendation here:
In Agent's bin directory execute run the agent script with the "setup" option. This should make the agent repeat the configuration dialog, so you can re-enter agent-server connection settings.
If this does not solve the problem, try this:
stop the Agent
delete the data directory
restart the Agent
Simon, will you try this and see if it solves your problem? thanks.