Unrecognized Configuration Section system.servicemodel Error in Machine.config

Unrecognized configuration section system.serviceModel
Could not load type 'System.ServiceModel.Configuration.BindingsSectionGroup'

After installing .Net 3.5 SP1 on the existing server, that runs .Net 2.0, I've got the exception:

I manually updated 2 lines in Machine.config based on Machine.config from my development machine, that didn't have the problem.

<!--<section name="bindings" type="System.ServiceModel.Configuration.BindingsSectionGroup, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>-->

<section name="bindings" type="System.ServiceModel.Configuration.BindingsSection, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

<!--<section name="extensions" type="System.ServiceModel.Configuration.ServiceModelExtensionsSection, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>-->

<section name="extensions" type="System.ServiceModel.Configuration.ExtensionsSection, System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>