Error: "You cannot change costing method because there are one or more ledger entries for this item."

Hi,

I am using NAV 2013. I was trying to use Configuration Package tool to update some Item Unit Price. 

I imported the template but it shows me error. For each uploaded record, it says "You cannot change Costing Method because there are one or more ledger entries for this item."

But, we didn't change the Costing Method.

Can someone help?

Thanks