Without knowing more about the specifics of the control in question, I don't see anything explicitly wrong with the code.
Just a few questions:
1) What is the reason for using "Keys" to select the item from the control list? Is there a method like "ClickItem" or something similar?
2) If it's a checklist box control, then there may be other methods. According to https://support.smartbear.com/testcomplete/docs/reference/test-objects/controls/desktop/dev-express/vcl/check-list-box/methods.html, there may be a method of "CheckItem" which will set the state of a particular item in the checklist box. Have you investigated other methods?
3) Let's get down to it. What type of control is it? Can you post screenshot of properties and method so we can assist further?