Using the Search API?
Access to the Search API is measured by the IP address the request is coming from. In large offices and at events or conferences, it is common for many people to share the same IP address and in some of these cases, our rate limiting may be too strict.
As users, the best thing for you to do is perform your search from twitter.com/search. If you continue to have problems searching Twitter at an event, follow the instructions on this page to help us improve the service.