The application you are using ran into a problem.
If you let their support team know about this error, please give them a link to this web page as well!
The application transitioned to a new URL, but the Url.Parser.toUrl function could not handle it. It probably is an unsupported URL like a file:// or data:// URL but it may be a bug in the elm-lang/url package. Explore more and report an SSCCE if you can definitively show it is a bug.
You can get more detailed information if you can reproduce the error in dev mode.
Hopefully that helps!