'Microsoft.SharePoint.Client.Taxonomy.TaxonomyField' does not contain a definition for 'GetWssIdsOfTerm'

I am trying to get the WSSIds for Terms to generated the CAML query. I am getting the error in the following line of code that 'Microsoft.SharePoint.Client.Taxonomy.TaxonomyField' does not contain a definition for 'GetWssIdsOfTerm'

int[] idArray = TaxonomyField.GetWssIdsOfTerm(_sourceSite, _termStore.Id, termSet.Id, tempterm.Id, false, 10);

In fact, I can find it on the internet that this static method is available. But why is it not present in the Assembly?

http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.client.taxonomy.taxonomyfield.getwssidsofterm

Please Advise.