Steve,

It is from Access Help:
*-----
Once you enter data in a table, you can't change the data type of any field to AutuNumber, even if you haven't yet added data to that field.

Add a new field, define its data type as AutoNumber , ....
*-----------------

>I couldn't find a category that fit my question so I just stuck it in this category, which is probably wrong, but I thought this category is better than nothing.
>
>Anybody know how to AutoNumber a field in Access when the database is already populated, but the field column I want to AutoNumber is blank, empty, or null?
>
>Microsoft Knowledgebase says, "I don't think so." Database must be new, blank database to do AutoNumber.
>
>I could make a spreadsheet and AutoNumber a spreadsheet column and then Update Query the Access filed column, but I was thinking there must be another way.
>
>I tried writing an Access Update Query to do it, but I cannnot get it to work yet.
>
>Thanks for your help.