This is possible with old batches of stock. Before taking any further action please try pressing F8 on the part number within Stocked Parts Maintenance. To correct this do the following:
Go to Stock
Click on Stocktake
Press F4
Select 'Confirm By item'
Untick 'Include Raw Material' , and select the part number in the range.
F5 on the new snapshot
Press Ctrl+M and click Add to Item
Enter all the relevant information, ensuring the batch number is the same.
Enter the absolute value in the 'Counted Qty' column. (If the negative is -10 then you will want to type in 10 to reverse it)
Hit Confirm Item
Once you have done this you will have to have a change made to your data as the stock quantity will not match the total of your batch quantities. The reason for this is the figure that you have just corrected will now be added to your stock quantity.
Should this not have worked, please raise a new case online and reference the title of this article.