Refreshing your browser is all we need to let the program accept the vendor's EIN, elliotahdcp.
To start, kindly click the Reload icon beside the site's URL. If the same thing happens, open a private window and access the 1099 e-file service site for Intuit Online. If you're able to enter the vendor's EIN without getting an error, go back to your previous browser and clear out the cache.
Once done, close and reopen the browser for the changes to take effect. You can also use a different browser to enter this information on the vendor's profile.
Please keep me posted with the results. I'll be right here if you need more help.