Thanks for suggestions. I've already installed the Turbine plugins. But it still doesn't work. When I use the call as Fortunis suggested, I get the same error but in the main.lua. All other plugins work perfectly. I suppose the file structure or naming is wrong. My directory looks as follow
Code:
Plugins
+->Fido
+-> simple.plugin
+-> simple (directory)
+-> __init__.lua (is empty)
+-> main.lua
+-> Window.lua
Fido