error message "It is already opened exclusively by another user, or you need permission to view its data." when I try to open Access mdb?

The ASPNET worker process doesn't have the correct permissions to connect to or write to the Access database. Either enable impersonation for users or configure the ASP.NET worker process to run under the SYSTEM account. You can also grant read and write permissions for the "Everyone" group on the database and the database folder.