Problem/Bug DETECTED OLD PLAYER DIRECTORY IN THE WORLD SAVE

hi, i wan´t to set up an old 1.72-bukkit server after a long pause. So i updated to bukkit 1.12.2. After that i am getting:

Code:

20:09:31 [SEVERE] Conversion failed, please try again later
20:09:31 net.minecraft.server.v1_12_R1.NameReferencingFileConverter$FileConversionException: Could not convert file for USERNAME
20:09:31 [WARNING] **** DETECTED OLD PLAYER DIRECTORY IN THE WORLD SAVE
20:09:31 [WARNING] **** THIS USUALLY HAPPENS WHEN THE AUTOMATIC CONVERSION FAILED IN SOME WAY
20:09:31 [WARNING] ** please restart the server and if the problem persists, remove the directory '.\World\players'

If i delete this folder, all userdatea is lost. I have acutal Java installed on Windows 10 64bit. Can i manually convert the player.dat-files?

 

thx- I now runned vanilla server 1.12.2 and it worked - all playerdata converted.