Don't worry, Mummified. I'm here to help.
I've got a few troubleshooting steps here for you to try to get you back on track. I know being able to create statements is an important part of managing your business, especially when you have as many customers as you do!
I'd like you to start by checking for data damage to your company file. The update may have jogged something out of place, and using the steps in the following article, you can check for any damage and learn how to resolve any issues. Take a look here: Resolve data damage to your company file
The next thing I'd like you to try is creating the statement a different way than you currently are. I suspect you've gone through the Customers menu in the top toolbar and chosen Create Statements. Here's another way to do it. After clicking Customers, go to the Customer Centre. Now, right click on a customer name and choose Create Statements to see if the program recognizes your have a customer when you try to create from them directly.
Lastly, re-sort the customer list to see if that'll help the program recognize your customers. Do this from the Customer Centre. While there, select View in the menu bar and then Re-sort List.
If QuickBooks Desktop still doesn't seem to understand that you do in fact have customers after all of these steps, call our phone support team for further troubleshooting. The team can be reached at 1-877-772-9158. Pro and Premier support agents can help at your convenience as the line is open 24/7. Enterprise support is available Monday to Friday between 9 a.m. and 8 p.m. EST. Learn more about potential support costs here: Intuit QuickBooks Desktop software support policies
Enjoy your day!