You're not providing much useful information, same with the other guy even if that's all he can get, so you're going to have to reinstall Blockland. Here's some things you can do to prevent save or addon loss:
Copy your Addons, Saves, Screenshots, and Config folders to another one.
Reinstall Blockland
Remove those folders in the new installed Blockland, then put the old ones in their place.
Note: Your config folder may be the root of the problem, same with the addons folder, so do the steps above again if you are still having this problem after the reinstall except keep one of these folders out of the process and experiment to see which one is the issue.