I'm not sure what error message you are getting.
Here’s what we recommend:
First, the Primary owner of the brokerage account must be logged on to import the information. Then, make sure you have selected the Vanguard brokerage account and not the mutual funds account. Customers have found that when they click on the Vanguard icon in the Select financial institutions section, it didn't give a choice of brokerage or mutual funds. However when they typed in Vanguard instead of clicking on the icon, they did get a choice and were able to select brokerage.
To import from your Vanguard account, please follow the steps below: