Import of tax rates fails with error "Invalid file upload attempt"

In this case the uploaded CSV file headers are not matching the store-views of the Magento installation. To fix this, follow these steps:

1. Open your base import file in a text editor
2. Navigate to “Sales → Tax → Import/Export Tax Rates” and click on [Export Tax Rates] and save the file on your hard disk and open it with a text editor
3. Replace the first line of your base file with the first line of the file you exported from your Magento installation. Your exported file will have your store views included, which is required to import the file properly.