Multi-Page not display, redirect to first page!

I have a new problem with multi-page article.

when click to Page 2 (or other page) the link http://www.sample.com/category/postname/2 automatic redirect to http://www.sample.com/category/postname (display the first page) and is impossible to access to other page

Where is the problem?? htaccess???? help me please

thanks