Whenever you see this problem in particular product, you should check product query option till current date. If you see difference in stock as on and current balance, you can run correct balance from product query itself to rectify current stock of this product.

This problem happens when due to some disturbance, program is interrupted in between and stock files are not updated properly. If you see this problem in many products, you can go to System->System Maintenance menu and run Balance Validation option.

There are different questions, if you have missing batch from product master or stock dates are wrong in detail file etc. You can select accordingly. Most of the time, stock mismatch problem is solved by first option only. If you select more options, it takes more time to complete. Please do not break or quit this option in between. Please run only when you have enough time to complete it.