Why isn't this working? Creating a dynamic movieclip using ActionScript

When I click the button, I want the “sand” movieclip to be created at position (200, 100). But when I launch the project I get an error:

The class or interface ‘sand’ could not be loaded.

However, even though I get thise error, the ‘sand’ movie clip which is placed on the application during design time does show up.

And when I click the button I trace the x position of the new movieclip and all I get is “undefined”.

Help please…?