Are you running 10.5.6 of Mac OS X Leopard or Mac OS X "Server" Leopard?

It does sound like a permissions error. Are you running the Now Server Manager in an administrator account?

The Now Server Manager stores the servers it creates in the following directories:

/Library/Application Support/Now Software/Event Servers/
/Library/Application Support/Now Software/Contact Servers/

You might try deleting both those directories and trying again.

Another thing you might want to try is uninstalling the Now Server Manager, removing the entire /Library/Application Support/Now Software directory, then restart the computer, reinstall Now Sever Manager and then try importing or creating a new server.
Sean Boiarski
Product Manager, Now Software