Error opening [URL]: Get [URL]: x509: certificate signed by unknown authority

[Nantris]

When running the tool from the server the site I am trying to index resides on, I get the error:

Error opening [URL]: Get [URL]: x509: certificate signed by unknown authority

Where [URL] is the URL of the site.

When trying to run from another server I have to that same URL I get:

Error opening [URL]: Get [URL]: remote error: internal error

Any ideas? Thank you!