MissingMethodException: Method not found: 'System.Xml.XmlReaderSettings.set_MaxCharactersFromEntities' with Matrix

I use Matrix from http://www.ag-software.net for XMPP. AG-Software team said that I should use http://www.ag-software.net/downloads/index.php?dir=MatriX%2FMono%2F3.5%2F&download=System.Xml.Linq.dll

But it doesn't work. I have error:

 MissingMethodException: Method not found: 'System.Xml.XmlReaderSettings.set_MaxCharactersFromEntities'.
 System.Xml.Linq.XDocument.Parse (System.String text, LoadOptions options)
 System.Xml.Linq.XDocument.Parse (System.String text)
 Matrix.Crypt.ElGamal.ElGamal.FromXmlString (System.String p_string)
 Matrix.License.License.Validate ()
 Matrix.License.LicenseManager.SetLicense (System.String lic)

They recommended to ask unity team about it:

The new Unity IL2CPP compiler has many bugs, the last we checked it wasn't able to compile MatriX properly to cpp code. So if you are using the IL2CPP compiler I ask you to contact Unity directly for support.