Here’s a call to SharePoint 2010 for creating a folder. Note the RootFolder.

// Build the CAML Query
System.Text.StringBuilder oSb = new System.Text.StringBuilder();
oSb.Append("     <Batch OnError=\"Continue\" RootFolder=\"\" >");
oSb.Append("         <Method ID=\"1\" Cmd=\"New\">");
oSb.Append("             <Field Name=\"ID\">New</Field> ");
oSb.Append("             <Field Name=\"FSObjType\">1</Field> "); // 1 = folder, 0 = document
oSb.Append("             <Field Name=\"BaseName\">" + folderName + "</Field> ");
oSb.Append("        </Method>");
oSb.Append("    </Batch>");
 
string sResult = oSb.ToString();
XmlDocument CAMLqueryXML = new XmlDocument();
CAMLqueryXML.LoadXml(sResult);
 
// Execute UpdateListItems
System.Xml.XmlNode result = lists.UpdateListItems(SPLibraryName, CAMLqueryXML);