Welcome to Community! It's important that you're able to complete your QuickBooks Online Payroll goals with confidence. The error you've described indicates the books have been closed for that period. Making changes can have a negative impact on your books, For this reason, I recommend reaching out to your accountant, for their expertise and best course of action. If you don't have an accountant, we can help you locate a ProAdvisor in your local area.
If you have any other questions, please feel free to reach back out. We'd be happy to help!