Because ryushare has a maximum daily download limit for free users. I think the message is pretty self-explanatory.
And it helps if you actually specify the host to get help since there are hundreds of them, I just took a best guess here.
I am experiencing a very frustrating problem though.. This happens to me for every download I try to make on ryushare now, and I haven't used it for some days now (Almost a week), so I'm practically blocked from downloading from this wonderful thread.