Hi,
When saving an stock entry repack, it shows an error ITC(Stock) is not an stock item.
Make sure the item that you have selected is a stock item,if not make sure to check the maintenance stock checkbox in the item doctype.
when check the maintain stock check box, it is showing an error:
As there are existing transactions against item ITC, you can not change the value of Maintain Stock
You already have transactions (purchase order, receipt and invoice) against that item.
Duplicate it, and enable 
maintain stock before proceeding with any transaction.
You can then disable the old item.