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https://help.tallysolutions.com/docs/te9rel61/Tax_India/Excise_Mfg/Serial_Number_x_already_exists.htm

Serial Number 'x' already exists

Cause

This message is displayed when the Prevent duplicate? option is enabled in the Excise Book master and you re-use a Rule 11 serial number for recording an excise sales transaction.

Solution

Rule 11 serial number should be unique for each excise transaction and hence Tally.ERP 9 prevents re-use of Rule 11 serial number. However, you can set the option Prevent duplicate? to No in Excise Book master and re-use a rule 11 serial number.