QuickBooks is giving me an error code when I attempt to enter a new invoice. ??

Thanks for visiting the Community, @wayneleske. 

It's possible the browser has too much historical data from previously visited web pages. This might be the reason you're seeing an error code when you enter an invoice. 

Let's perform some steps to help get rid of this error. You'll first have to access your QBO account through a private browser. It's a great way to help isolate the issue since it doesn’t store data in the cache. If you're using Google Chrome, press CTRL + Shift + N on your keyboard. Hit CTRL + Shift + P for Mozilla Firefox and Internet Explorer. Press Command + Shift + N if you're using Safari.

From there, create a test invoice. If it works, go to your regular browser and clear its cache. This helps the browser to boost its performance when accessing QBO. If not, I'd suggest using other supported browsers. 

Once your client pays the invoice, here are the three options on how to record the payment: 

• Use the Receive Payment feature.
• Click the New transaction drop-down menu from the All Sales page.
• Go directly to the customer profile.

You can always run the Transaction Detail By Account report. This lets you get a list of all invoices that are due on a particular date. Just go to Reports from the left menu. Then, enter the report name in the Search box. For detailed steps on how to pull up and customise this report, visit this article: Generate An Invoice By Due Date Report. 

If the steps above don't make any difference, I'd appreciate if you can share with me the specific error code. This helps me provide you an appropriate solution to fix it. 

I'm here anytime you have other concerns. Have a good day, @wayneleske.