Having troubles running your Access 2000/XP apps on Access 2003? This is due to the new security settings in Access.
Update: Instructions for Access 2007
For the full version of Access:
Open Access 2003 from the start menu. Go to Tools->Macro->Security... (you may have to "reset" your toolbar if this menu does not show up. Tools->Customize->Toolbars Tab->Reset)
On the dialog box that opened up, select "Low", then click "OK"
For Access 2003 Runtime:
Set or create the following registry keys:
If you need to keep your security settings at Medium or High, then you will need to obtain or create a digital signature for your application.
More information about signatures can be found here.