Except as provided in s. 71.80 (25), a Wisconsin net operating loss may be carried back against Wisconsin taxable income of the previous 2 years and then carried forward against Wisconsin taxable incomes of the next 20 taxable years, if the taxpayer was subject to taxation under this chapter in the taxable year in which the loss was incurred, to the extent not offset against other income of the year of loss and to the extent not offset against Wisconsin modified taxable income of the 2 years preceding the loss and of any year between the loss year and the taxable year for which the loss carry-forward is claimed. In this paragraph, “Wisconsin modified taxable income” means Wisconsin taxable income with the following exceptions: a net operating loss deduction or offset for the loss year or any taxable year before or thereafter is not allowed, the deduction for long-term capital gains under subs. (6) (b) 9. and 9m., (25), and (25m) is not allowed, the amount deductible for losses from sales or exchanges of capital assets may not exceed the amount includable in income for gains from sales or exchanges of capital assets and “Wisconsin modified taxable income” may not be less than zero.