403 Forbidden Error when trying to use Twitter Card Validator


I’m getting a 403 Forbidden Error when trying to validate my Twitter cards at https://dev.twitter.com/docs/cards/validation/validator. I cannot explain this error as no other crawler has ever had a problem accessing my site and it is accessible fine through a browser. The URL I am trying to validate is http://www.dealsunited.net/

I’m not sure why a 403 Forbidden Error would be encountered. I thought maybe the robots.txt file had some kind of exclusion, but even after removing that for testing purposes, the error remained.

Has anyone else experienced the same problem?