Last few new customers i have tried to invoice when i hit send an error message shows up saying i must select a customer but it won't add the new one i have just typed in

Hi there,

It's vital that you're able to invoice your customers. Don't worry, I'll be happy to help troubleshoot this.

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. Give this a try and let me know how you make out. 

If you're still having issues, feel free to send me a screenshot of what you're seeing on your screen. I'll be here in case you need further assistance.