Message: ...ace\AddOns\SimpleILevel_Group\SimpleILevel_Group.lua line 178:
Division by zero

Weird, I don't get the same error with the beta, but i'm not in a group there.

But I do see the issue, perhaps groupsize should be initialized as 1 on line 160, although the for loop would need changed. Otherwize an if/else statement just prior to line 178.