Thank you for taking the time to visit the Community to report this issue.
At this time, I would recommend contacting support directly for a review of the logs to help determine the cause of this error message.
https://www.quicken.com/support#contact-support
As the connection type is Direct Connect, this will most likely need to be brought to the attention of the financial institution, Vanguard. However, support can help in locating the error message to provide them.
Thank you,
-Quicken Tyka