I'm working with the YamlDotNet library and I'm getting this error when loading a YAML file: While parsing a tag, did not find expected tag URI. The YAML file is supposed to be well-formed because it comes right from RoR. The error seems to be triggered by this code: formats: default: ! '%d-%m-%Y' long: ! '%d %B, %Y' short: ! '%d %b' I'm not an expert, but I see from the YAML spec that you can use