Hello,
As you probably already know, the sequence of setting up custom domain is described here: http://help.wildapricot.com/display/DOC/Custom+domain+setup
You forgot to perform step 1:
1) Add custom domain via Domain management
and we did this for you.
Unfortunately right now name admin.cpsquare.org is not recognized as a known name so high probably it was not properly registered by your ISP.
Vassily, Wild Apricot team