w3c validation API blocks my IP

hi,

If I check a page by your site, it returns result.
But if i do it from api, it returns 0 as status after some requests
and don't let me open http://validator.w3.org/ manually . Does sending
many requests blocks my ip? .
Is this due to continuous requests ? what is the solution ? how many
requests can be send in a period of time ?

Regards,
Nirzari,