Serialization error

[Pasztelyi]

After starting minetest and opening my world i got this message (please open my attachment).
Any idea how to solve this problem ?

[Krock]

Never seen this before. It's an interesting error because Minetest tries to load a backup file, means that either the loading function is broken or your system failed to write to a file.

0) Close Minetest
1) Open "path_to_minetest/worlds/your_worldname/players/"
2) Open all files which start with "singleplayer"
3) Find the file which contains the line "PlayerArgsEnd"
4) Remove all "singleplayer" files except the one you found above and rename it to exactly "singleplayer" without any further file extension
5) Start Minetest, hope that it works.

If there's no file with that line: Remove all "singleplayer" files and it'll be created on your next join with the default values. You might need to teleport back to the right location and re-fill your inventory.

PS: Also check whether you're using a recent Minetest release such as 0.4.17.1 (stable) or 5.0.0-dev (in-development).