directory name not valid when installing

Hi Everyone

I’m using Cpanel to install wordpress via fantastico.

When I typed in the directory name and go to the next step; the following message appeared:

– No valid directory name provided.

I don’t want to install wordpress under the root because there is already a website there.
So I typed in the directory name as http://domain.com.au/blogtesting/

If directory blogtesting is not exist, usually it will auto create right? but it says not valid; so I’m not sure.
Btw there is also no similar name in the directory folder; I checked it.

Please help out.