General Support: Plogger on subdomain problem

Hello! I thought it would be much better to start my own gallery for my photos, rather than a flickr photo stream...
Could I have been that misled?
The situation is:

1) I created a subdomain, using the OPS Subdomain Mapping tool, and creating a /gallery/ folder outside my main htdocs, which has its own /htdocs/ inside, thus making my root something like:
/htdocs/
/gallery/htdocs/
The subdomain worked fine, and the test index page I uploaded appeared every time someone visited the subdomain.

2) I uploaded the Plogger files into the /gallery/htdocs/ folder and run the Plogger installation. Which completed in success.

3) I log into Plogger.

4) I see the Plogger option tabs - BUT...

Whenever I try to click on any of these tabs to manage my galleries (...Manage/ etc) I get sent back to the login screen - where I am asked to log in again and so on and so on...
I am not using any .htaccess because I thought the easy way would work this time.
Do you think this could be messing up my Plogger funtionality?