Cannot prorate to Zero

Hi All,

I am facing a scenario when I could not import invoice through open interface. Lets say I have following invoice details:

Line 1: ITEM, Amount = 100

Line 2: ITEM, Amount = -100

Line 3: FREIGHT, Amount = 20

Line 4: TAX, Amount = 2

Invoice Total: 22

Prorate Tax and Freight = Y

I am getting this error: CAN'T PRORATE ACCROSS LINES THAT SUM TO ZERO 

Shouldn't it be imported properly where it is freight only scenario ???

Please advise..

Regards,

MH