Unable to assign client roles to specific user

I am using keycloak:11.0.0, and trying to assign the roles of specific client to a particular user and i get below error.

**10:20:46,881 WARN [org.keycloak.services.resources.admin.ClientRoleMappingsResource] (default task-707) org.keycloak.storage.ReadOnlyException: Not possible to write 'role mapping for role ’ when updating user