What does "You can't change the lock assignment for the sales account director. (ZCA-210018)" mean?

Summary:

Content (required):

User is removing a resource from the account team and encountered this message. I am still trying to replicate it but would like to as in general what the message means?

I already tried searching knowledge in MOS but found no related articles.

Version (include the version you are using, if applicable):

22D

Code Snippet (add any code snippets that support your topic, if applicable):