Zmias1 Does this happen in a new save? Please test for comparison's sake and let me know. The unique rewards are tied to your account, not to any particular save. The consumable rewards (e.g. potions) are given to sims in your active save, but if that bothers you, it's easy enough to complete the tasks in the new save and then claim the rewards until you're back in your main save.
If you can't complete event tasks in a new save, please test again with your Mods folder removed. If that doesn't help either, please provide a dxdiag. Click Windows key-R, enter dxdiag in the run box, wait for the scan to finish, click "Save all information," and save the file to your desktop. From there, you can attach it to a reply using the paper clip (Attachment) icon included with the other formatting buttons.
