Public Function CreateFolder(ByVal FolderUrl As String, ByVal SPList As Microsoft.SharePoint.SPList) As SPFolder
Try
Return Me._CreateFolder(SPList, FolderUrl)
Catch ex As Exception
Return Nothing
End Try
End Function

Private Function _CreateFolder(ByVal targetList As SPList, ByVal folderUrl As String) As SPFolder
If String.IsNullOrEmpty(folderUrl) Then
Return targetList.RootFolder
End If
Dim folder As SPFolder = targetList.ParentWeb.GetFolder(targetList.RootFolder.Url & "/" & folderUrl)
If (Not folder.Exists) Then
If (Not targetList.EnableFolderCreation) Then
targetList.EnableFolderCreation = True
targetList.Update()
End If
Dim folders() As String = folderUrl.Trim("/"c).Split("/"c)
Dim folderPath As String = String.Empty
For i As Integer = 0 To folders.Length - 1
Me.GetValidFileOrFolderName(folders(i), "_")
folderPath &= "/" & folders(i)
folder = targetList.ParentWeb.GetFolder(targetList.RootFolder.Url & folderPath)
If (Not folder.Exists) Then
Dim newFolder As SPListItem = targetList.Items.Add("", SPFileSystemObjectType.Folder, folderPath.Trim("/"c))
newFolder.Update()
folder = newFolder.Folder
End If
Next i
End If
If folder Is Nothing Then
Throw New SPException(String.Format("The folder '{0}' could not be found.", folderUrl))
End If
Return folder
End Function

Private Function GetValidFileOrFolderName(ByRef path As String, Optional ByVal replacementChar As Char = "_") As Boolean
Dim illegalPathChars As New RegularExpressions.Regex("^\.|[\x00-\x1F,\x7B-\x9F,"",#,%,&,*,/,:,<,>,?,\\]+|(\.\.)+|\.$", RegularExpressions.RegexOptions.Compiled)
If path Is Nothing Then
Return False
End If
path = illegalPathChars.Replace(System.Web.HttpUtility.UrlDecode(path.Trim()), replacementChar.ToString())
If path.Length > 128 Then
path = path.Substring(0, 128)
Return GetValidFileOrFolderName(path, replacementChar)
End If
Return path.Length > 0
End Function

E la versione C#