exclusive lock on local Symmetrix

It's difficult to say without knowing your full configuration, but it doesn't appear to make a lot of sense on the surface. It may be a matter of wording though.

Masking doesn't actually put a lock on the Symm itself, but it does require exclusive access to the SymAPI database on the host with the SDM agent. I have run into issues before when I'm trying to mask devices from the CLI on my SDM agent host. ControlCenter has a temp lock on the SymAPI database (I assume as it is polling for DCPs) and I have to retry the commands after the polling cycle completes. I would have thought that if you were issuing the masking commands from ControlCenter that it would be smart enough to know if it was conflicting with itself though.

Are there other admins who might be running commands at the same time through CLI or SMC?

no one have access to ecc server except me , and no one have symcli

so does my ecc version 6 conflict with itself

I've seen this behavior before. What I usually did was wait half a minute and issue the command again. When the errors was still there I tried from another host. It looks like the local db is locked for some reason and that's why trying it on another host might just work.

I know it's not a very good solution, but it just could work.