xAuth problem: consumer key and secret don't work


I have a problem: every time I try to authorize my application I get an 401 error. I’ve tried different solutions, then I tried to replace my consumer key and secret with someone’s else and surprisingly the app works. How can I solve this problem?
Here is my OAuth details:
Access level Read and write
About the application permission model
Consumer key xxxxxxxxxxxxxxxxx
Consumer secret xxxxxxxxxxxxxxxxxxxxxxxxx
Request token URL https://api.twitter.com/oauth/request_token
Authorize URL https://api.twitter.com/oauth/authorize
Access token URL https://api.twitter.com/oauth/access_token
Callback URL http://smarturl.it/notizie
Sign in with Twitter Yes


Are there details included with the 401 error? Does the key you’re using have permission to use xAuth?


No, there are no details. What do you mean with permission to use xAuth? Do I need a permission?


Yes – xAuth requires explicit permission from Twitter to be able to use. Permission is only granted to applications that have no other means to secure web-based authorization (such as environments where a web browser is completely unavailable). Most modern applications and operating systems provide some means to perform web-based authorization, so it is seldom awarded in the present day.