Cascading Combo Boxes (Extended Cut)

Kevin's Cascading Combo Boxes video is definitely the right place to start.

What you're seeing is normal behavior for a Continuous Form. It looks like each row has its own combo box, but Access is really displaying the same set of controls repeatedly. When you change the employee combo box Row Source for the selected harness key, you change it for every displayed row. That is why employees assigned to the "normal" keys disappear.

The practical solution is to filter the employee list while also including the employee already assigned to that particular record. In other words, the Row Source should include:

1. Employees with the required harness certificate

2. The employee currently assigned to that record

That lets you prevent a new invalid assignment while keeping existing assignments visible.

Also, Microsoft has just added native cascading combo box support to Access forms, including Continuous Forms, without needing VBA. I believe it is currently in the beta channel and should reach the Current Channel once they have worked out the bugs. If you need a solution now, follow Kevin's method in the Extended Cut. If you can wait a month or two, native Access support may make this much easier.