Steps I followed:
1. Parked parkedsite.com
2. Created subsite on Multisite (www.multisite.com/parkedsitedirectory)
3. moved plugin into site for install
4. moved sunrise to wp-content folder
5. moved domain_mapping.php to mu-plugin folder
6. updated wp-config file and set sunrise to on with define snippet
7. set domain mapping to my http://www.multisite.com pinged IP address
8. set my site id (parkedsite id = 2) and domain name to "parkedsite.com"
Tried to go to the URL. I don't think I left any steps out but I was very thorough.
Hope this helps narrow things down..