Hello densch :)
I've got an idea! Are you sure that you've installed the FONT provided in the game folder? It's called "Hippopotame.ttf". If the font is not installed, the game fails to calculate the length of the text. This could be the cause of your problem!
I just added a warning message to the game in case the game font is not installed, so that other players won't encounter the same unintelligible error message as you. This will be available in the next release.
The simpler the better, so I'll have to think of a way to directly use the font present in the game folder without bothering the player with font installations -_-