Let me share the steps to add your catch-up contribution and resolve the error message you've gotten, @mjoycthomas.

When setting up a retirement plan for your employees in QuickBooks, you can only choose one deduction for your 401k contribution. If you've already set up a 401k contribution, this may be the reason why you're receiving an error message when attempting to add the catch-up contribution.

That said, you'll need to delete the other contribution that you've already set up. Let me guide you on how:

1. Go to the Payroll tab and select Employees.
2. Select the employee's name.
3. From the Deductions & Contributions section, click Edit. 
4. Choose the deduction you want to remove by clicking the Trash bin icon.

Once done, you may want to add a new 401k Catch-up retirement plan. See the steps below:

1. Go to the Payroll tab and select Employees.
2. Select the employee's name.
3. From the Deductions & Contributions section, click Edit. 
4. Click the + Add deduction/contribution.
5. In the Deduction/contribution dropdown arrow, select the + Add deduction/contribution.
6. Choose Retirement plans in the Deduction/contribution type.
7. On the Type dropdown, choose 401 (k) Catch-up.

For more details about setting up deductions in QuickBooks, see this article: Set up a retirement plan.

Moreover, I'll include these links about the yearly retirement plan contribution limits and managing payroll reports:

• Retirement Topics - Catch-Up Contributions
• Run payroll reports

Please know that you're always welcome to comment below if you have other concerns or follow-up inquiries about managing your contributions in QBO. I'm just around to help. Take care always.