Cost Variance in average costing method

Hi,

One of our customer is using average costing method in inventory.

As per my knowledge ,if quantity derived negative quantity then the cost of the item will hit to cost variance account.y i

we are not allowing to derive the negative quantity in inventory.

For few of the transactions the balances moved to cost variance account.

How this can be possible in average costing method.Is there any other scenarios which will hit to cost variance account.

Please help us to resolve the issue.

Thanks

Rama Devi