If you're using NTFS, the first thing I would check is file permissions. Access is a file-based database system; so the users connecting through IIS must have Change NTFS rights to the .MDB file in order to update it. If users do not authenticate to gain access to the site, you need to grant Change access to the IIS anonymous user. If you're concerned about security, you should be! This weakness is the reason most sites rely on client-server database systems like SQL Server 2000.
If your Web server connects to the Access database via a network share, also verify that the share has been configured with Change access.
This was first published in May 2001