Apending and Updating from a form

I don't think my last question was clear. I have an Employee table, a Course
table and a Registration table to connect the employees with the classes. I
was looking for a way to add more than one employee at a time to a class. I
have created a yes/no select box in my employee table and made a subform
(from a query) with EmpID, Name, and the select box. The main form is the
rest of the information needed for registration such as class name, date
taken, complete or incomplete and so on. I created an update query and an
append query and here are my problems:

When I run the update query it unchecks all the boxes however I can't do
anything else because it tells me a related record is needed in the employees
table. Can't see why.

When I run the append query it adds a registration (autonumber) and the
employees I selected, however, it doesn't add any of the other information on
the rest of the form such as the class info.

Am I going about this the wrong way? Or am I missing a link?

Thanks for any advice.