Can't set PropagatedNamespaces for XmlDsigC14NTransform

Can't set PropagatedNamespaces for XmlDsigC14NTransform. This is my source code:

XmlDsigC14NTransform^ c12n = gcnew XmlDsigC14NTransform();
System::Collections::Hashtable^ hashtable = gcnew System::Collections::Hashtable();
hashtable->Add("xsi", "http://namespace");
c12n->PropagatedNamespaces = hashtable;

Under c12n on the last line it says:

System::Collections::Hashtable ^System::Security::Cryptography::Xml::PropagatedNamespaces::get()

Error: property "System::Security::Cryptography::Xml::PropagatedNamespaces" (declared in "C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Security.dll") has no 'set' accessor

This is very weird because in XmlDsigC14NTransform Class description it says "Gets or sets a Hashtable object that contains the namespaces that are propagated into the signature" under PropagatedNamespaces property.

I'm using Visual Studio 2013 and the project has been set for NET Framework 4.0.

Is there any way around it?