I am having this same error for Voltz, Hexxit, Tekkit, except all I can do is Tekkit Lite, Yog Box and Hack/Mine. Here is the exact error it gives me when I run Big Dig:
Error unzipping a file for the following pack: Big Dig
error in opening zip file
Please consult the modpack author.
I am running on a Windows 8 Toshiba. I would prefer not consulting the modpack author so can u guys help me?