Hi,
Did you change the IP address from Network Connections or via the SBS wizard? You should have done the latter. If you did it manually then you should change it again using the SBS wizard.
If you did this using the SBS wizard and it is not working, you should perform some additional diagnostics on the DC. 'dcdiag' and 'dcdiag /fix' may help.
If you open a 'nslookup' prompt on the client does it resolve addresses quickly? If you look up 'yourdomain.local' does it return the correct server IP?