Please use DoFolderBrowserDialog, DoOpenFileDialog and DoSaveFileDialog to manipulate external files.
After using these methods (from TimeLine.Client.Framework.Tools.FileDialogHelper) the path that was selected is saved in TL.INI, TLSYS section, EXPORT_PATH attribute in order to be used next time the open file dialog is called. The same is done when using the xButtonSearch with BrowseFile mode, or exporting data from a DxDataGrid.