Add to cart redirect link doesent work.

I assume you mean you set the redirect URL through the Ubercart UI at admin/store/settings/cart ?

Ubercart has automated test cases to verify that this setting works as designed. Those test cases don't indicate a problem, so this is likely something specific to your site. If clearing the cache fixes it, you should look first at anything on your site which modifies Drupal's default caching behavior such as the Boost module or a distribution like Pressflow. Of course, check your server logs and your Drupal logs. And when your redirect breaks, examine the uc_add_item_redirect variable in the {variable} table to see if the value has changed.

No further info provided.