looking at this screenshot from you:
I can see it is missing a X in the column with the header 3 and as well in the columns with the header 6 and C
I think the most important missing entry is the X in column C, which means your unit has no indicator for commercial unit. Without being a commercial unit it must not be used in a purchase order. So somebody has removed this indicator from your unit H after it was already used in purchase orders.
So the only way to solve this problem is to make the unit again a commercial unit. You will find the indicator in the detail of your unit H in transaction CUNI