I have a test site (because I can't get it working on the actual live site).
I have set up the mu site, and tried adding http://blog.cookislandinfo.com/
The page is blank, I can't see the dashboard, also blank. I have installed it as per instructions, but what I am not clear about, is the settings for the a/cname etc. the options I have, don't have the same options as listed in your instructions.
The domain name is with discountdomains.co.nz - I have these options:
use discountdomains nameservers
modify A/MX/TXT records
set up url forwarding
under Modify a/mx/txt records, i have
cookislandinfo.com > IPv4 (A) > our ip
http://www.cookislandinfo.com > IPv4 (A) > our ip
I added :
* > IPv4 (A) > our ip
blog.cookislandinfo.com > IPv4 (A) > our ip