Error installing software with PostgreSQL 9.1 and Stack Builder

I used PostgreSQL 9.1 Server in my Windows XP computer.
It has the application Stack Builder option.
I got an error when trying to install additional software with Stack Builder 3.0.0.
I posted the screenshot of the error I am receiving.
Please send some help so I can fix the issue.
Thank you.

Stack Builder Error
Failed to open the application list:
http://www.postgresql.org/applications-v2.xml
Error: the URL specified could not be opened.
OK
