[bdbxml] Substring indexing

Hi
I am trying to do substring indexing. My listIndex looks like this:
Default Index: node-element-substring-string

However, when I do a lookup on dbxml shell, I dun get any answer. I am 
putting the node name also in my search
lookupIndex node-element-substring-string "" "name" "" "" "Zinc"

However, it gives me no result. But, there is an entry which has the text 
"Zinc or Iron".
Any ideas why isn't it working and how to make it work.

Regards
Manish