Mac OS X Lion Server :: Network Accounts Do Not Iogin

last month our Xserve G5 with Leopard Server which controlled user accounts in our computer labs died. We replaced it with a Mac mini server (that includes Lion Server) –by the way, this is the first server that I ever setup–.During initial configuration, the server was fully updated to Lion server 10.7.3, and stablished as an OD Master. I didn't import anything from the old server, so all accounts and groups and preferences and everything have been defined from scratch.Everything was working good until I finish the setup and try to connect from one of our Leopard client machines. I configure that machine with Directory Utility with settings from the server, and the server responds just fine, the client sets everything up automatically for authentication and contacts. Everything seems to be normal until I log out and try to connect with one of the network accounts.The account will not login, the login window just shakes and does nothing. Odd enough, the login window tells that network accounts are available (captures are in Spanish). When I login again as a local admin account, I check Directory Utility and when I look at the LDAP configuration, in the search & maps tab of the window, I find these two red registers (UserAuthenticationData and OLCLDIFConfig). I don't know if this is related to the problem, but this is where I get stuck and don't know where else to go.

Info:
Mac mini, Mac OS X (10.7.3)