Why do people on this site who have so little to import think their sophomoric opinions have merit, as in "just import manually". Turbo Tax has been going down hill ever since they hired more lawyers and fewer programmers. It's getting to be a larger waste of money and less value every year. A management change is required.
I have posted on this problem as well. Not only could I not import 1099-DIV from Vanguard, but importing a PDF directly into TT resulted in numerous errors.
I pay a premium for TT because it advertises the ability to import 1099's from Vanguard but when it does not work I'm told to "input manually". I've had more problems with TT this year that any of the past 20 years.
Start by checking if your financial institution or brokerage is a TurboTax 1099 partner (opens new page; scroll down and select the 1099/1098 Partners tab). If your institution isn't on the list, you won't be able to import.
Make sure you're selecting the correct partner in TurboTax. Some have similar-sounding names but are actually separate entities. For example, J.P. Morgan Chase Bank, J.P. Morgan Funds, J.P. Morgan Private Bank, and J.P. Morgan Securities are all listed as TurboTax partners, and if you choose the wrong J.P. Morgan, you won't be able to import. Also, some entities may use a different name for investments. Be sure to check with your institution to determine what company their investments are being held under.
Once you've confirmed that your institution is a TurboTax 1099 partner, make sure you're using the proper sign in credentials on the import page, and that you have a working internet connection. A wired connection, if available, may be more stable than wireless.
For more 1099 import troubleshooting suggestions, click that link. @Pip_12_mn