I'm determined to ensure that your taxes are withheld without a hitch, @SteveDonoho.
First, let's run the payroll update to ensure that you have the latest tax table version.
Do you know if these employees are meeting the wage bases set by the IRS? You can click on this link to learn the wage base limit: Topic No. 751 Social Security and Medicare Withholding Rates.
If you're getting the same result, it's possible that their W-4 status has been set to 'Do Not Withhold' by mistake. Here's how to check if an employee was set to Do Not Withhold (Exempt):
You can check out this article for more information: 0.00 or no income tax withheld from paycheck.
To give you more troubleshooting steps on what to do if payroll taxes are not calculating, please visit these resources:
Please let me know if you need further assistance with payroll. I'm always around to help. Have a good one.