Was MGRM's decision to use stack-and-roll hedges the reason for its colossal losses? What risks cannot be hedged with stack-and-roll hedges?

What will be an ideal response?

The stack-and-roll hedge is a technically sound way to hedge commodity price risk. The hedger is still confronted with basis risk (i.e., the risk of a change in the difference between the spot price and the futures price), but this risk is usually less than spot price risk. If the position being hedged is massive enough, changes in basis can cause sizeable cash outflows.
Stack-and-roll hedges protect annual income statements when hedge accounting is permitted. If the company has to use lower-of-cost-or-market accounting, the annual income statement is not protected by stack-and-roll hedges. Stack-and-roll hedges do no protect against credit risk.