Domain mapping - Subsite Broken link

Hi guys,

We setup our main MultiSite blogs as http://blogs.ntu.edu.sg. And the site blogs to be http://blogs.ntu.edu.sg/xxx , where xxx is the blogs name. or it can even be http://blogs.ntu.edu.sg/yyy/xxx, where yyy is a group name.

For example:

http://blogs.ntu.edu.sg/xxx-> http://blogs.ntu.edu.sg/administration or http://blogs.ntu.edu.sg/schoolofengineering

http://blogs.ntu.edu.sg/yyy/xxx -> http://blogs.ntu.edu.sg/schoolofengineering/it-depart or http://blogs.ntu.edu.sg/schoolofengineering/mechanical-depart

We like to used this Domain Mapping and give
http://blogs.ntu.edu.sg/schoolofengineering/it-depart to become http://it-dept.edu.sg.

We have set accordingly to the instruction. But, we found out, http://blogs.ntu.edu.sg/schoolofengineering/mechanical-depart or even http://blogs.ntu.edu.sg/administration are affect and become broken site.

We need advice on where has we gone wrong.