Better suggestion;
back up what you know works. Including backing up your saves, and your screenshots in a new folder, because Blockland automatically overwrites them. (starts at 1, so when you make a new one and you already have a screenshot labeled 1, it will replace it.)
You may also want to back up your Serverprefs.cs and your avatar favorites. Possibly also Add-Ons you know worked, and also you could try playing in single player and then hitting the ~ key to see if you get any errors.
By backing up I mean making a folder tree going from
(Directory):/Blockland/Add-Ons/
Or (Directory):/Blockland/Base/Data/(all of the stuff after that)
And also (Directory):/Blockland/(every folder after that.)
