This will be due to the roles that your staff are assigned and what each role has been granted access to.
First of all, go to ‘Administration’ > ‘User Roles’ and check to see which roles have ‘Can Access PM Module’ turned on. If you need to turn it on for a particular role you can do so by clicking ‘Edit’ and putting a tick next to ‘Can Access PM Module’. Click ‘Save’ and then repeat this for every role you wish to edit.
Next, go to the ‘User Accounts’ tab and check what roles have been granted to your staff. You may then need to switch back to the ‘ User Roles’ tab to adjust the ‘Can Access PM Module’ option for other roles.