Did you send yourself the document URL or copy and paste the URL in the address box? Unfortunately, the URL in the address box isn't stable. You need to grab a persistent URL (more information about document URLs can be found in our Article Linking Guide). If you did grab the document URL, the URL should have https://vanguard.idm.oclc.org/login?url= at the beginning. If it doesn't, try adding that text before the document URL:
This URL will force your computer to access the database through the library's proxy server, and the database will then recognize that you are a Vanguard University user.