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

Source : mscorlib

Message : An error occurred creating the configuration section handler for system.serviceModel/bindings: Could not load type 'System.ServiceModel.Configuration.BindingsSectionGroup' from assembly 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

Filename : c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Config\machine.config

Line : 100

Errors : System.Configuration.ConfigurationException[]

Stack Trace :

Server stack trace:

   at System.Configuration.BaseConfigurationRecord.EvaluateOne(String[] keys, SectionInput input, Boolean isTrusted, FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentResult)

   at System.Configuration.BaseConfigurationRecord.Evaluate(FactoryRecord factoryRecord, SectionRecord sectionRecord, Object parentResult, Boolean getLkg, Boolean getRuntimeObject, Object& result, Object& resultRuntimeObject)

   at System.Configuration.BaseConfigurationRecord.GetSectionRecursive(String configKey, Boolean getLkg, Boolean checkPermission, Boolean getRuntimeObject, Boolean requestIsHere, Object& result, Object& resultRuntimeObject)

   at System.Configuration.BaseConfigurationRecord.GetSection(String configKey, Boolean getLkg, Boolean checkPermission)

   at System.Configuration.BaseConfigurationRecord.GetSection(String configKey)

   at System.Web.Configuration.HttpConfigurationSystem.GetApplicationSection(String sectionName)

   at System.Web.Configuration.HttpConfigurationSystem.GetSection(String sectionName)

   at System.Web.Configuration.WebConfigurationManager.GetSection(String sectionName)

   at System.ServiceModel.Configuration.ConfigurationHelpers.UnsafeGetSectionFromWebConfigurationManager(String sectionPath)

   at System.ServiceModel.Configuration.ConfigurationHelpers.UnsafeGetAssociatedSection(ContextInformation evalContext, String sectionPath)

   at System.ServiceModel.Configuration.ClientSection.UnsafeGetSection()

   at System.ServiceModel.Description.ConfigLoader.LookupChannel(String configurationName, String contractName, Boolean wildcard)

   at System.ServiceModel.Description.ConfigLoader.LoadChannelBehaviors(ServiceEndpoint serviceEndpoint, String configurationName)

   at System.ServiceModel.ChannelFactory.ApplyConfiguration(String configurationName)

   at System.ServiceModel.ChannelFactory.InitializeEndpoint(String configurationName, EndpointAddress address)

   at System.ServiceModel.ChannelFactory`1..ctor(String endpointConfigurationName, EndpointAddress remoteAddress)

   at System.ServiceModel.EndpointTrait`1.CreateSimplexFactory()

   at System.ServiceModel.EndpointTrait`1.CreateChannelFactory()

   at System.ServiceModel.ClientBase`1.CreateChannelFactoryRef(EndpointTrait`1 endpointTrait)

   at System.ServiceModel.ClientBase`1.InitializeChannelFactoryRef()

   at System.ServiceModel.ClientBase`1..ctor()

I've searched the Google and the post  http://social.msdn.microsoft.com/Forums/en-US/wcf/thread/bde7c986-25c3-443b-9d8e-db8579ae1478 suggested to use ServiceModel Registration Tool (ServiceModelReg.exe)  .But it didn't help.

With a hint from post Unrecognized configuration section system.serviceModel

I manually updated 2 lines in Machine.config (that probably were left from some previous beta installation) 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"/>