This unfortunately is due to the save being from too many versions behind. It won't be possible to safely continue the character from where you left off.
But, if you want to keep their stats, clothes, items, and skills you can try this:
-- Open the old game folder. Open www > img > faces
-- Locate "p-zbrow1.png" and also "p-zbrow1.rpgmvp"
-- In a second window, open the new game folder. Open www > img > faces
-- Copy these two files from the old game into the new game
-- In the new game folder, go back to the main folder (Lust Doll Plus r48.1) and run Game.exe
-- Load your character, open the menu, go into Sanctum, head left and use New Game+