I want to save some presentation file as images into some directory and use the code:

    OpenFileDialog o = new OpenFileDialog();
    o.ShowDialog();
    if (o.FileName != null)
    {
        ApplicationClass pptApplication = new ApplicationClass();
        Presentation pptPresentation =  pptApplication.Presentations.Open(o.FileName, MsoTriState.msoFalse,
        MsoTriState.msoFalse, MsoTriState.msoFalse);
        FolderBrowserDialog fb = new FolderBrowserDialog();
        fb.ShowDialog();

        for (int i = 0; i < pptPresentation.Slides.Count; i++)
        {
            pptPresentation.Slides[i].Export(fb.SelectedPath + "Slide" + (i + 1) + ".jpg", "jpg", 320, 240);
        }
    }

use namespaces:

using Microsoft.Office.Core;
using Microsoft.Office.Interop.PowerPoint;

But i get the following error:

'Microsoft.Office.Interop.PowerPoint.ApplicationClass' does not contain a definition for 'Presentations' and no extension method 'Presentations' accepting a first argument of type 'Microsoft.Office.Interop.PowerPoint.ApplicationClass' could be found (are you missing a using directive or an assembly reference?)
Tho it seems that it has property called Presentations..
What am i doing incorrectly?