An employee is not able to track times - what is not working?

Please review if the corresponding employee is "Time Tracker" and "active". These settings you can adjust in the employee administration as an administrator.
An employee can only track times for projects he is assigned to. Please review if the employee is assigned to the corresponding projects he wants to track times. Watch out if there are eventually set time restrictions, which could affect the possibility of tracking times.
Take care that your project assignment of the corresponding employee is set to active(tick mark).
Also be aware of setting your customer or project to active.