What are you currently doing on this page to associate the user with the client? If you are ensuring that the user must be logged in first and that the userID is held in a session variable then you should be using this session variable when inserting a client.
Please describe what you are doing on this page and how you are associating the id. Also, in the db what is the value that is held in these records for the user and client? Please also post back with a copy of the page in question so it can be reviewed.