I can help you get rid of the error message, joe20.
Unexpected responses in QuickBooks can sometimes be caused by too much cache in your browser. Let's see if this is the case.
Open your account using a private browser to see if you can successfully save an invoice. Please see these keyboard shortcuts depending on the browser you're using:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari: Command + Option + P
If it does, I would recommend clearing the cache of your default browser. This removes excessive files preventing the program to work properly. Also, you can use another supported browser as an alternative.