I'm a little confused here, possibly because I don't run Access 2007, but you say you have
" a field which stores Client names, it is a lookup to a value list."
A Value List in previous versions of Access is just that, a list of values you enter into the Row Source of a combobox/listbox that has Value List selected as the Row Source Type.
A combobox/listbox that draws its data from a field in table, as your post suggests yours does, has a Row Source Type of Table/Query, and in order to add items to it you must add records to the underlying table. You cannot, I suspect, simply use the "Edit list items" feature.
BTW, it's always a good idea to give the version of Access you're using when posting a thread, especially when using v2007, as many things are new/different in this version.
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