This is most likely to happen where you're using an Access database and you do not have permission to update it. This can be due to the user permissions on the folder it resides in, perhaps because your web host has moved you to a new server.

You need to set the permissions on the folder to allow the internet user to modify it.

But also, check your connection string - it's possible to configure this in a way which means the database is opened in read-only mode.