Cannot delete this item because there are existing purchase order item

Hi

I tried to delete an item, so I did these steps:
1- I saw a message which said that there was some transactions which is linked to this item,
then I delete all transactions which are using this item that I want to delete.
2- new message is:

So, I go to " Purchase Orders Inquiry " and search in the name of the item with all history.
But nothing was there.

Any suggestions.

regards

Adel