My swagger UI displays and it is showing all of my routes. Everything looks great except there is a big red ERROR indicator on the lower right. When I click it I get:

{
  "schemaValidationMessages":[ 
     {
       "level":"error",
       "message":"Can't read from file http://devxxxx.com:80/swagger/docs/v1"
     }
   ]
}

How do I fix this error?

That's the validator badge. The error is most likely because the on-line validator can't reach the OpenAPI spec on your server (devxxxx.com). I am assuming this server is behind a firewall.

Depending on the version of Swagger UI, you may be able to disable the validator badge. In 2.x, you can simply add validatorUrl: null to the SwaggerUi constructor in index.html. In 3.x, there have been problems disabling the validator badge. For more details search for validatorUrl issues over on GitHub.