ACC2000: Can't Change Combo Box Value If ControlSource AutoNumber

Novice: Requires knowledge of the user interface on single-user computers.

This article applies to a Microsoft Access database (.mdb) and to a Microsoft Access project (.adp).

If the ControlSource property of a combo box is set to a field that has an AutoNumber data type or that is automatically populated, you receive the following message on the status bar when you try to change the value in the combo box:

The control source of a combo box is a table field where Microsoft Access writes your combo box selection. Modifications to an AutoNumber or an automatically populating field are not allowed. Therefore, if the ControlSource property of a combo box is set to one of these fields, Microsoft Access cannot update the value in the field; therefore, you cannot change the combo box value. Microsoft Access gives you the message to tell you why it cannot update the combo box control.

Either change the data type of the field in the ControlSource property of the combo box, or set the ControlSource property to a field that does not have an AutoNumber or an automatically populating data type.

Steps to Reproduce Behavior

1. Start Microsoft Access, and open the sample database Northwind.mdb.
2. Create a new table called MyTest:

      Table: MyTest
      ------------------------
      Field Name: MyAutoNumber
         Data Type: AutoNumber 
      Field Name: MyData
         Data Type: Number
      Field Name: MyBucket
         Date Type: Number
   					

3. Open the MyTest table in Datasheet view and enter a few records by typing numeric values in the MyData field. Note that Microsoft Access automatically fills in the MyAutoNumber field and puts zeroes in the MyBucket field as you type values in the MyData field.
4. Create a new blank form in Design view based on the MyTest table.
5. Add a combo box to the form and set the following properties:

      Combo Box:
         ControlSource: MyAutoNumber
         RowSource: MyTest
   					

6. Switch the form to Form view. Note that the combo box values are the sequential numbers coming from the MyAutoNumber field.
7. In the combo box list, try to select a new value. Note that you receive message on the status bar, and the value in the combo box does not change.
8. Switch back to Design view and change the combo box ControlSource property from MyAutoNumber to MyBucket.
9. Switch back to Form view and repeat step 7. Note that now you can select items from the combo box. If you look at the contents of the table, you can see that the values thatyou selected were written to the MyBucket field.

For more information about combo boxes, click Microsoft Access Help on the Help menu, type Combo boxes: What they are and how they work in the Office Assistant or the Answer Wizard, and then click Search to view the topic.