The type or namespace name 'Data' does not exist in the namespace 'System'

[Tim Scott]

I am using Spark in a library assembly to generate templates for email
and such. It's working fine when called from my application.
However, when I try to call it from a test, I'm getting this:

error CS0234: The type or namespace name 'Data' does not exist in the
namespace 'System' (are you missing an assembly reference?)

1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4 using System.Data;
...

The config in my test is identical to the config code from my app
(where all is well). I know that because I copied it. My test
project indeed does reference System.Data. Everything is .NET 4. Any
ideas?

The the way, I do not need System.Data in my templates. I am not
adding this namespace in my config. It's being added automatically by
Spark I guess.

[Tim Scott]

Ignore my last statement about my not setting System.Data namespace.
Still, I don't understand why I get this error.