Why do I get "URL is not Valid" when trying to add an asset?

There are 3 scenarios as to why the CMS is unable to access the content.

1. The DAM system could be down. Please check with your systems administrator if you suspect that is the issue.
2. The content is set to Private. You will need to make sure links are publicly accessible for our CMS to access the content.
3. The asset no longer exists in the DAM.