The exception is raised in the following line of the code:
SecurityContextToken sct
=        client.IssueSecurityContextTokenAuthenticated(token, issuerToken);

The exception is the following:
uncontrolled exception of type 'System.Web.Services.Protocols.SoapException'
en microsoft.web.services2.dll

additional information: System.Web.Services.Protocols.SoapHeaderException:
Server unavailable, please try later --->
System.Configuration.ConfigurationException: WSE032: There was an error
loading the microsoft.web.services2 configuration section. --->
System.Configuration.ConfigurationException: WSE040: Type
WSSecureConvService.CustomUsernameTokenManager, WSSecureConvService could not
be loaded. Please check the configuration file.
  at System.Web.Configuration.HttpConfigurationRecord.Evaluate(String
configKey, SectionRecord section)
  at System.Web.Configuration.HttpConfigurationRecord.GetConfig(String
configKey, Boolean cacheResult)
  at System.Web.Configuration.HttpConfigurationRecord.GetConfig(String
configKey, Boolean cacheResult)
  at System.Web.HttpContext.GetConfig(String name)
  at
System.Web.Configuration.HttpConfigurationSystemBase.System.Configuration.IConfigurationSystem.GetConfig(String configKey)
  at System.Configuration.ConfigurationSettings.GetConfig(String sectionName)
  at
Microsoft.Web.Services2.Configuration.WebServicesConfiguration.Initialize()

Any help will be great.
Thanks.