The method you follow is fine, but you've got problems with the scale and orientation of your objects.
Lets start with the Curve.
- Make sure its Origin (A, the orange dot) is located at one extremity of the curve. Otherwise, make them fit in Edit mode.
- Make sure its Scale (B) is (1 1 1) and Rotation is (0 0 0): otherwise, in object mode, press Ctrl+A / Rotation and scale.
Now we'll set up the plane and its modifiers.
- Make sure the plane's origin is at the same location than the curve origin : in Object mode select the Curve, Shift+S / Crursor to selected. Then add the plane.
- Make sure the plane is oriented like the yellow ones in my picture. Make sure its Scale is (1 1 1) and Rotation (0 0 0), or Ctrl+A/Rotation and scale.
- Add an array modifier. In Fit Type, select Fit Curve, then select your curve. Crank up the offset to space them a bit.
- Add a Curve modifier, select your curve.
You should obtain something very similar than the grey planes in my picture. If not, check every step again...
Let's add the box:
Select the plane, Shift+S / Cursor to selection, Shift+A Cube.
You'll want to resize it : please, do that in Edit mode ! I'm pretty sure 90% of your problem is that you resize/rotate in object mode.
It should be oriented like in my picture.
Once again, Ctrl+A/Rotation and Scale
Make the box a child of the plane, activate Dupliface on the plane. Tada! Once you're here, you'll probably want to disable Render Instancer (so only the boxes will be rendered, not the planes).