I agree with Karthik - you should export the old configuration into a text editor and re-work it for the current syntax with respect to NAT and how you assign the physical interfaces.
Also if you have any access-lists on the outside interface they will now use the real IP address of the target host vs. the NATted public IP.
The command parser is capable of reading an old syntax configuration upon startup and converting it, but you cannot just paste the old syntax into a running appliance.
A migration like this is a good opportunity to clean up the old configuration and reinforce your understanding of all the functions and features you have configured in your firewall.
