Zone Entry Limit?

I'm trying to add a huge number of entries into a new zone to apply to a firewall rule I have created. I get two errors, failed to read firewall config and failed to change settings. Just curious what the maximum, or recommended max number of entires should be. And is that per zone, or would that be for the entire config file? (XML export)

The zone I'm trying to enter has 43,041 entries. This is "US Only" zone that has an entry for every known US IP subnet. I don't want anyone outside the US trying to connect to this particular service.