Oh, we're basically against having proper or sane error messages. Insane error messages build character!
 

There are several ways and they were often discussed.

The problem stems from this being a curried error, meaning it comes from elsewhere. This time from the YAML module.
The YAML module said it failed, and we're currying the error it indicated. Unfortunately that error is not very understandable.

Like I said, we did discuss how to make these things easier for end-users. One suggestion by Dams was to check YAML ourselves and provide a proper error message. However, this would become quite difficult in Dancer 2 since it will have various configuration engines (to allow you use to JSON, INI or other formats you might like more than YAML). We would not be able to write our own meta-parsers for each format and check it before the actual format parser parses it. It's not very clever.

Instead, another way is to provide a cleaner more understandable output when YAML fails. Unfortunately we can't always control how it failed. We do try to make it clear it's the parser by writing "Unable to parse the configuration file". We're more than open on any suggestion you may have on how to make this easier.

So, unfortunately this is much less of a "Dancer problem" and more of a "YAML problem".