Can't populate foreign key field?

[satone]

I'm building a database that, among other things, relates records in a CHILD table to those in a PARENT table via an ID#. (The ID# happens to be a concatenation of three other fields in the PARENT table.)

The thing is, I entered 20 records in the PARENT table and about 35 related records in the CHILD table before I discovered the beauty of foreign key fields!!

So anyway, I set up a foreign key field in the CHILD table. I know I did something right b/c, when I look at the 35 or so pre-existing records in the CHILD table, I see the drop-down list and can select ID#.

HOWEVER when I create a NEW record in the CHILD table, I do NOT see a drop-down list next to ID#. No field, no box, no nothing....

So......

Wondering what I'm doing wrong? Any thoughts?