Knowing what version you were on would help. As would knowing the step that's failing. But I assume that there is a connectivity problem with the agent - either agent to server or server to agent.
Validate from the agent configuration that it is seen by the server. It's online. In newer versions you can run an explicit communication test. In older versions you can go to the agent's variable screen as that used to be pulled on each request rather than cached.
Then go to System -> Server Settings and find the connectivity URLs that are passed to the agent. Ensure that you can hit those URLs - exactly as they are on that screen - from the agent. If you can't, the agent won't be able to hit the Server's web services and you would see some sort of connectivity error - perhaps like this one.
Knowing what version you were on would help. As would knowing the step that's failing. But I assume that there is a connectivity problem with the agent - either agent to server or server to agent.
Validate from the agent configuration that it is seen by the server. It's online. In newer versions you can run an explicit communication test. In older versions you can go to the agent's variable screen as that used to be pulled on each request rather than cached.
Then go to System -> Server Settings and find the connectivity URLs that are passed to the agent. Ensure that you can hit those URLs - exactly as they are on that screen - from the agent. If you can't, the agent won't be able to hit the Server's web services and you would see some sort of connectivity error - perhaps like this one.