MuleSoft Maven Build Error "Could not transfer artifact" or "Failed to read artifact descriptor"

You are using Maven to manage your dependencies and build your projects with MuleSoft. You are attempting to build your project but get an error about Maven not being able to find the dependencies in the Mulesoft Enterprise repository, though it's a custom dependency and shouldn't be found in the Mulesoft repository. The error message looks something like this:

[ERROR] Failed to execute goal on project PROJECT_NAME: Could not resolve dependencies for project com.mycompany:project_name:mule:1.0.0: Failed to collect dependencies at your.package:artifact:jar:1.0.0: Failed to read artifact descriptor for your.package:artifact:jar:1.0.0: Could not transfer artifact your.package:artifact:pom:1.0.0 from/to releases-ee (https://repository.mulesoft.org/nexus/content/repositories/releases-ee/): Not authorized , ReasonPhrase:Unauthorized. -> [Help 1]

Maven errors are sometimes cryptic and seem to suggest Maven is not looking in the right place, but actually one simply defines all repository locations, and Maven looks in all of them, including your Maven local repo in .m2, to try to find them. 

This error is caused by the fact that, as Maven is not finding the dependency, it's trying to look for it in the Mulesoft Enterprise Nexus repository as the last resource, then fails because of not being able to find it. This actually has nothing to do with the Mule repositories or Mule Maven Plugin.