This error specifically occur when the Service field is blank while attempting to make the time billable to your customer, bekl.
You can uncheck the Billable (per hour) box, which eliminates the need to enter an item in the Service field. Here's a screenshot showing how I encountered the same error as you did:

Afterward, you'll be all set to process payroll for your employees.
Feel free to share more details you need further assistance with this.