Cannot alter unit for Item x

The aforesaid error generally appears while :

Uploading "StockItem Masters" into a Tally Company; which already contains the same StockItem but with a different unit of measurement.

Here's a example :

StockItem with name "Item A" exists in Tally Company having Unit of Measurement (UOM) as "Nos". Let's now try to modify it's UOM to Kgs. As you can see below, the cursor does NOT go the the Unit field.

Remarks:
This is a restriction in Tally Software. You cannot alter the UOM of a StockItem if one or more records / vouchers exist which contain that StockItem