Adding Xsellize source can be tricky. The source brings some really cool apps for FREE.
You need to generate a username+password to add this source. To get the username and password you will have to register on www.xsellize.com and then use the same username-password in the source.
It goes something like this. If your username is wxyz and your password is 123456 then the source you have to add is http:// cydia.xsellize.com/wxyz-123456.