This type of error tends to mean that the agent tries to get information from the server about Fixlets, properties, actions, etc, but it gets back a response it didn’t know how to deal with. It is possible that this would indicate an issue on the server/relay but if it is only this one computer, it might be a different problem. You might want to double-check you are using the right masthead file and you might try running the BES Client Diagnostics tool.
If you can’t get it working, I suggest you send the Client Diagnostics output to the support team and they should be able to figure it out.