[2020] Can't connect to singleplayer, only multiplayer

In that case sending your logs to support@strangeloopgames,com after you tried to load / create a world would help: https://github.com/StrangeLoopGames/EcoIssues/wiki/Getting-the-Eco-server-and-client-log-files-for-local-world

Likely reasons are a corrupted mods folder (remove it and verify integrity afterwards) or any changes made to WorldGenerator.eco, as via ingame you can only generate default worlds with no changes.

There is no way to fix this ourselves as this issue is not caused by us. I'm glad the instructions helped you two, though :)

It's not any changes, but any changes that make the world bigger, as the singleplayer uses the 32-Bit server and any size bigger than default size will exceed the RAM limit for it and therefore crash. As we do not recommend and support changing config files that cannot be altered on world generation for singleplayer, i kept it short. If you want to change stuff manually, please start the server manually via EcoServer.exe (which is the 64-Bit one).