Why can't I access Server.app in Lion Server? I can't access Server.app in my mac mini server, i don't know why.
The username and password are correct.

How can I solve this problem?
I found a problem, the servermgrd was not running, I was search in Active Monitor and no found it.  

To resolve just run:  

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.servermgrd.plist