I installed the markdown plugin but the preview doesn't work.

I tried to create a new file and set the file type as markdown from Document menu.I tried to save a file with .md extension, but in either cases I the preview doesn't show anything.

I tried to click right mouse button on the preview panel and click refresh and I obtained this error message:

Error opening file /home/mirko/index.html: No such file or directory

I need some help