the red excamation point only means that Dreamweaver does not recognize something. It may be a problem, it may not. If it runs OK in the browser, then you can ignore it.
If I ignore the exclamation point and try to run from the server I get the two errors first noted. It seems (according to the errors) that the eCart object isn't being found (per your reference to the include statement).
the require once line is a relative link to the ecart file in the WA_eCart directory, you may need to play with it to get the relative path ot go down the required number of directories to get to the root of the site.
I understand that -- I think the site structure is okay when the Dynamically-related files error doesn't appear in DW. There are no page sub-directories (other than those created by the WA extensions). Apparently DW and running on the server see the same error as indicated by the exclamation point. Am I correct in presuming that the error means the cart object isn't available? FWIW -- I am using cookies to store the cart.