Login temporarily blocked is an error that is caused when you use the incorrect login info. Note two things: 1) You were sent an email when you bought your server with the correct login info. It should be titled "Your Minecraft Server has been setup," if you do not see it, check your spam folder. 2) Your Multicraft login info is not the same as your client area login info.
To fix the error: 1) Use the correct login info. 2) Clear your browser cache/cookies. 3) Use another browser. 4) Wait 5 minutes.