Are you using a Cookie or Session persistance cart? Maybe it needs a:
It should set a session variable on the add to cart page, and access it on the cart page to go back to the correct page, so if sessions aren't working then this functionality may not work.
Another possibility is that the eCart redirect code isn't on the page... Does the eCart object show with a red exclamation point in the server behaviors window? If so there may be a missing piece of code causing the problem.