DTD is prohibited in this XML document when using CSOM with SharePoint Online -

this code snippet

string strusername="abc"; string strpassword="123"; securestring sspwd = new securestring(); strpassword.tolist().foreach(sspwd.appendchar); clientcontext context = new clientcontext(siteurl); sharepointonlinecredentials credentials = new sharepointonlinecredentials(strusername, sspwd);  context.credentials = credentials; // sharepoint web @ url. web web = context.web;  // want retrieve web's properties. context.load(web);  // execute query server. context.executequery(); 

creates following error message trying connect sharepoint online:

for security reasons dtd prohibited in xml document. enable dtd processing set dtdprocessing property on xmlreadersettings parse , pass settings xmlreader.create method.

the same thing happens using sharepoint client browser downloaded codeplex (https://spcb.codeplex.com).

what's wrong? can do?