Thats all ok. Please check if the paths to the named configuration files etc. under System > Server Config > DNS are correct.
If thats the case, then there might be a problem with the dns record you created as ispconfig does not write the dns record when bind refuses to load it e.g. when the zone has no ns records or the ns records does not exist as a-records etc. You can see such errors by enabling loglevel debug, then modifying the dns records and check the log a minute later.