PROTECT error

I try to run below two statements

Set tRS = ##class(%ResultSet).%New("%Dictionary.ClassDefinition:SubclassOf")
​set tSC = tRS.Execute("%Persistent")

and I always get <PROTECT>check+5^%Dictionary.ClassDefinitionQuery.1

The login user is _SYSTEM and should have all the permissions.

I cannot run queries in the $SYSTEM.SQL.Shell(). I would get <PROTECT>%GenerateMetadata+16^%SQL.StatementMetadata.1

However, when I run the query through SMP, everything is fine.

Any idea where could I start to investigate ?

Thanks.