Access 2003 Table with Unique ID's

I have 2 Tables that I use for my form, TM which is the primary table and has a Primary key assigned to the field EXEID. I also have a table called Discussion which I have a field called DiscussionID that is an auto number. The Discussion table is a subform on the main form page. My problem is that it won't give the DiscussionID a unique number, it is using the EXEID as the number. When I tried to set the DiscussionID to no duplicates, I can only put in one record and the next one gives me an error. Any help would be greatly appreciated.