The following error is consistently being displayed on the Package Server:
Package Server is configured to publish HTTP(s) codebases, but could not access it's own Web site.
ITMS 8.x
Certificate in the personal certificate store was found to be expired, even though it was not the certificate bound in IIS it was generating the error.
Removing the expired certificate from the personal certificate store resolved the issue.
Also, verify that the port 443 binding in IIS Manager is using the right certificate or that it is not expired.