Why would I be getting this error if not using a datasourceid?
If you have gotten this error before then you probably just migrated your ASP.NET application to a different server with a different database name. I am using Linq to SQL in my code and I think that is where this cryptic error message comes from.
Don’t look at the answer marked as the answer. Look down the page to the entry by keef_riff_hard. He states
What you need to look for is NOT that you have both the DataSource and DataSourceID defined – but rather see if the value for the DataSource is bad.
This was my issue; bad connection string. Fix it and everything is happy! 🙂