Problems with Validator

Trying to use the validator for testing various resources. I am getting errors about various URLs aren’t resolving. For example:
Canonical URL 'http://hl7.org/fhir/us/core/StructureDefinition/us-core-immunization' does not resolve

If I drop this url in my browser, it resolves just fine.
I’ve tried setting the java environment variable to use my system proxy settings
(-Djava.net.useSystemProxies=true), and including my proxy as an argument (-proxy …), but no luck.

Am I missing something?

If you want to perform validation that depends on artifacts from an implementation guide, you need to pass a “-ig” parameters to the validator listing the relevant IG(s). Without that, the validator only has awareness of the content defined in the FHIR core specification for the specified version.