In SAP system any tcode can be locked (means user can’t execute the transaction ) or unlocked. SAP provides a control level transaction – SM01 which helps to lock/unlock any other transaction.
Execute Tx- SM01
It displays all SAP Tcodes. Which transaction wants to be locked just check the check box and uncheck the checkbox to unlock any transaction.
To see all licked transactions, press F6 or navigate along the shown menu path.
List of all locked transactions.
SAPCODES 
Replaced by SM01_CUS since release 751
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