situation(1):

  IEdmStrLst5 pathList = default(IEdmStrLst5);

  pathList = vault1.BrowseForFile(this.Handle.ToInt32());

  IEdmPos5 pos = default(IEdmPos5);

  pos = pathList.GetHeadPosition();

  string wkFilePath = pathList.GetNext(pos);

   App.Workbooks.Open(wkFilePath);---> Success

situation(2):

  string wkFilePath = 'C:\MyVault\Data\Test.xls'

  App.Workbooks.Open(wkFilePath);---> Error (File Not Found)

  How To Use condition 2, will succeed,  Thank you.