@jvarughese23 - as long as no transactions have been processed, then yes.

@StevenRatner Thank you .. In this Case  can we un assign the class from items to get the option activated .. will this affect in anyways in case the item already have Lot or serial Information in it . what is the best practice to update this 

@jvarughese23 - This usually happens because the Lot/Serial Class has already been used in transactions. Once the class has been used, certain fields are locked to prevent inconsistencies in the data.