I was having the same issue.  Once the employee accepts the invite and creates an account the employer is no longer able to change the employee's email address.  This account now belongs to the employee.  The employee will have to log into their Workforce account and change the email address.  Have the employee sign into Workforce and click the Gear in the upper right corner.  They should be directed to an Email Notification page with a message that reads Your pay stub notification emails are sent to XXXXX@XXXXX To change your email, visit your Intuit account settings here.  <Click here.  They should be directed to a page that reads Hello (Employees Name)! Under Quick Actions click on See More.  Click on Change Email. 

I hope this helps.