if your capital account went negative which it apparently did things get complicated. you should have reported a negative capital account as capital gain the year it went negative and each year thereafter that the negativity increased. MLP as a rule showed capital a/c's in schedule L on the tax basis (inside and outside basis are the same). the fact that ending capital is zero is because the MLP plugged withdrawals and distributions to make it come out zero.
TT can not handle a negative cost and neither can most pro software. you have a significant tax issue see a tax pro.
