If you are experiencing this error, it means that at some point, you've added the license key to a Mister Horse account.
When a key is added to the Mister Horse account, the key no longer works. However, you do not need it anymore, to use the product you only need to be logged in.
To use your products with your Mister Horse account, do the following:
1. Login to Animation Composer.
2. Open the "Manage Products" section.
3. Download your products if necessary.
Then the products should work fine.
If you cannot see your products in the Manage Products dialog, please make sure you are using the right Mister Horse account.