not the first time
Hey - You're the fourth person to report this error so far -
I'm trying to figure out what causes it. Could you let me know what emulator you were running and describe how and when the bug took place? Did the bridge disappear, or did the map distort, removing walkable terrain? What was the lead character in your party? I'm trying to figure out if it's a graphics related bug or just something dealing with certain emulators. Did you save your game before the bug, or only after? With a savestate or on the rom memory save slots?
ah- how rude - I'm asking questions before offering solutions. and my response is a month late.
So far there are two fixes.
you can either use a game genie code to walk over seawater (can't remember what it is offhand, I think it's mentioned on another forum, romhacking.net I think)
Or you can use the overworld map editor in ffhackster (a hack program) to manually change the seawater to land. most of what I used to make the hack was done in ffhackster.
hopefully I can figure out what causes the bug and put out an updated version of the patch that will stop this error from concurring.