530 Authentication failed, sorry...HELP!!!

I can't login and it says:

Resolving host name yk.webzarray.intelhost.biz...
Connecting to (yk.webzarray.intelhost.biz) -> IP: 69.41.244.34 PORT: 21
Connected to (yk.webzarray.intelhost.biz) -> Time = 241ms
Socket connected waiting for login sequence.
220-=(<*>)=-.:. (( Welcome to PureFTPd 1.0.12 )) .:.-=(<*>)=-
220-You are user number 2 of 50 allowed.
220-Local time is now 22:16 and the load is 0.78. Server port: 21.
220 You will be disconnected after 15 minutes of inactivity.
USER YK
331 User YK OK. Password required
PASS (hidden)
530 Authentication failed, sorry
Cannot login waiting to retry (30s)...


What should I do?

although is says "User YK OK", either your username or password are wrong. double check them (reminding case-sensitivity) or contact the server administrator.

Thanks for your help!!!