The error 6000 typically occurs with QuickBooks Desktop (QBDT), @brattonbuilders.
Could you please provide more details about the error you've encountered? This information will help me assist you better.
In the meantime, you can clear your browser's cache so the system can start fresh. Being unable to send an invoice can be due to accumulated cache and doing this can help eliminate any stored webpage data that might be causing the problem. Also, make sure that you're using a supported browser.