Since I'm apparently not the only one with this issue, even after trying the fixes listed, I think we should all come together when asking for support. Please post in this thread if you have this same issue when trying to connect to the Runescape Client. When posting please list your OS, including 32 or 64 bit. Also include whether you've tried uninstalling all Java instances and reinstalling the client. Another issue that might be related is when running from the Jar sometimes you will not get the Agent error but instead the green start instance button might just dim and nothing happens.