I'm here to share additional steps to fix the issue, Nathan at Kasten.

Making sure your QuickBooks Desktop software is up to date should be our first step. This guarantees you have the most recent features and fixes.

To be sure, did you also receive the same trouble creating invoice for other sales order while using the Sales Order Fulfillment Worksheet? If not, you can open the affected sales order and ensure all the required details are filled out. 

If so, you can download and install QuickBooks Tool Hub to check for unusual errors and immediately fix them. 

Here's how:

1. Close QuickBooks.
2. Download the most recent version (1.6.0.3) of the QuickBooks Tool Hub. 
3. Open the file you downloaded (QuickBooksToolHub.exe).
4. Follow the on-screen steps to install and agree to the terms and conditions.
5. When the install finishes, double-click the icon on your Windows desktop to open the tool hub.
6. Select Program Problems.
7. Click Run Quick Fix my File.

For your reference, visit this link for the complete information on the process: Fix common problems and errors with the QuickBooks Desktop Tool Hub.

If the issue persists, I recommend contacting our QuickBooks Desktop Support. They have the resources to perform a screen sharing to further assist you in fixing the problem.

I'm including this article for a step-by-step procedure to create an invoice coming from a sales order for future reference: Create an invoice in QuickBooks Desktop.

Feel free to post again if you need anything else in QuickBooks. Have a great day.