Hi there,
Error messages like those aren't fun to deal with especially when you're trying to get some work done. Don't worry, I'll be happy to get you back on track so you can start enjoying the benefits of QuickBooks.
First, I'd like to start off by doing some troubleshooting to determine if this isn't a browser related issue. When was the last time you cleared cache and cookies on your browser? Doing this will help fix most issues the site may be having. Here's an article which shows you how to do that: How to clear Cache and Cookies. Let me know what happens after you clear cache and cookies.
If you're still having issues, I recommend contacting our support team using this link. One of our agents will be glad to take a look at your account and give you a hand with adjusting the invoice.