Blank page on Twitter authorization site using Struts and Java

I'm building a Twitter client on Java and Struts. I'm using the Twitter4j! library to make the connection.

Everything was working OK until 1 month ago. When the user needed to authorize the Twitter app and using the sendRedirect instruction, the browser shows a blank page. If I copy the开发者_StackOverflow link on a separate tab/window, it shows OK (https://api.twitter.com/oauth/authorize?oauth_token=XXX)

Why could this be happening?

Thanks in advance.