[twitter-dev] rate limits problem

i'm using reset api

http://api.twitter.com/users/show/{screen_name}.xml

and I also used OAuth token where added auth-token/secret key using a
super account from a certain app.
before yesterday, it worked perfect and successfully sent lots of
above requests( > 5000 ) per hour with different {screen_name}.

but it doesn't work well now, after request > 150 times, it always
returns :

Rate limit exceeded. Clients may not make more than 150 requests per
hour.

any ideas?

Thanks in advance.

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