S'43...."Error reading file"

[HirooOnoda]

I have no idea why I see this "error reading file" from my opponent.

We've explored every possibility-failure to end turn, both using the same version of the game, etc.

My opponent says when he tries to open the file the game requests my password. Very good.

But when I get the same file I get the "Error reading file."

What could cause this?