Calendar module access denied

Calendar module access denied

Hi
We subscribe to the zoho crm professional and I want to be able to see the zoho calendar module but it doesn't seem to be available; I get this error message when I click on the 1 day or 7 day icon;

Permission Denied
You do not have permission to view this component as corresponding module has been disabled in your profile settings (or) in Organize Tabs

How do I fix this?
Thanks
Marcus