The first question is "How User forgot to enter count for the material in year 2012 ?"
I think the stock was same as previous when PI performed. So the line item was not counted mistakenly..
Kindly inform your organization..
Check the all movement of material, check the stock for the material..
Check every thing for the material, if it is okay ?
Then go to MI02 and delete the line item for the PI document.