I wish there was an easy fix. Though it is weird that only a specific version (v0.3.6.4) had problems with its exported characters. I tried earlier with an export from v0.3.5.x and it worked just fine. Hopefully, you were able to get your character back. ^.^
Actually, it is very easy for me to
not lose characters (especially exported ones).
When I make or import a character (that I don't intend to throw away):
1) I start LT with a new/unused copy of "properties.xml" (in \data\);
2) Create or import the new character;
3) Make a Quick Save before finalizing the creation (Ex: Save just *before* I sleep or shower the first time with a new character);
4) Finalize the character for its first use;
5) Export the character and put copies of the Save and Export into another directory;
I have learned to keep 3 or 4 of the most-recent versions of LT (and copies of each properties.xml, character Quick Saves, and Exports) ... because bad things happen.
(And sometimes those things are even my fault!
)
(So, if anyone ever needs an old-but-recent version of LT, I might have one to share--just because.
)