Does this folder exist on your computer? If so, try deleting it.
C:\Users\Alec\AppData\Roaming\.minecraft\mods\zan
I usually end up nuking this directory whenever I start a new world just to get rid of old waypoints.
If you're playing a DW20 pack, it sounds like something is pointing to your old minecraft install dir and hopefully getting rid of this old dir may help.
Your mileage may vary of course, best option is as Wagon153 suggested. Hope you get it resolved soon.