What this indicates is that someone, or some thing, is trying to create a table in a schema that already exists.
Here is the structure of pg_class_relname_nsp_index: CREATE UNIQUE INDEX pg_class_relname_nsp_index ON pg_class USING btree (relname, relnamespace)
What you should also see in the error log is a line immediately following that error which shows you exactly what the conflict is, but you have not provided that to us.