Why is there no 'Create Client Portal' button?

There are two rules that might stop you creating a client portal or seeing the Client Portal button:

• You must be an admin or the owner of the project to create a Client Portal. Once created, anyone with access to the project can use it.
• The project must have a client defined on it (it may be worth adding this as a mandatory field within settings).
  

If both of these are set correctly, it is possible that you are not authorised to create or use client portals for that project type - an administrator can check this for you.