If you purchased the Encore-published Torchlight retail disc, after downloading the update, you may be prompted to enter a key.
This issue affects Windows users only.
Summary and Resolution
The retail distribution does not require a key. If you are getting prompted to enter a key, most likely you have applied the wrong patch to your Torchlight installation. To resolve this issue, reinstall Torchlight from the disc, download and apply the retail patch.