Not enough information, so I'll have to give you some generic tips.
Make sure you're typing it exactly right. Try not to confuse O with 0, S with 5, etc.
Make sure you haven't been sharing your key with other people. Your key will deactivate if it is detected that the key is being used across multiple IPs very quickly.
Make sure you're getting a good connection, specifically to
http://master2.blockland.us/. See if you can load that in your web browser.