Hi Mr. SAP,
Based on the diagnosis, you can figure out that most likely someone is already editing the customizing table or might you are not authorized..
In case if you have the access to SM12 Transaction code, kindly check if an entry present there. If yes it means the table is locked and you can't proceed on that. you have to reach out to the specific resource to unlock the table who did a lock, else you need to reach out to BASIS to make that entry delete.
Regarding authrization for locking of table, please check SU53 after the execution of the T-code, if you are missing any role. If you find anything there, then reach out to your Security team to get and assigned roles to your profile.
Regards,
Abhi