DbProviderFactories configSource error

If I try to add configuration->system.data->DbProviderFactories through configSo开发者_如何学Gource:

<DbProviderFactories configSource="FileName">

I get an ConfigurationErrorsException with message "Unrecognized attribute 'config source'"

What am I doing wrong?

system.data is a configuration section, so can have a configSource attribute. DbProviderFactories is an element within this section, and can't.