"StockItem already exists" error appears when we import the StockItems as shown below :

Here's the video that shows what happens when you import this data into Tally.
WRONG DATA
The aforesaid error appears if the StockItem Names are repeated (as shown below) :
| Item Name | Alias | PartNo |
| APPLE | A1 | |
| BALL | B1 | |
| BALL | B2 |
PS: The StockItem Name cannot be same for two different PartNos.
CORRECT DATA
The same error would appear if the Item Names are repeated (as shown below) :
| Item Name | Alias | PartNo |
| APPLE (A1) | A1 | |
| BALL (B1) | B1 | |
| BALL (B2) | B2 |
PS: The StockItem Name is now unique.