[SalesForce] Error: The ISCHANGED function cannot reference the RecordType.Name field

I am trying to prevent Recordtype from being changed for Account. when I use ISCHANGED( RecordType.Name ) in validation rule, the following error appears:

Error: The ISCHANGED function cannot reference the RecordType.Name field.
I have tried using different fields with the same error. I noted that the record type is another object. if this is the reason why I cannot, is there a suggestion as to how I can do this?

Best Answer

You should reference the lookup field on the object itself, rather then indexing across the relationship field. In this case, that would be RecordTypeId.

ISCHANGED() cannot reference fields on other objects; as you note, the Record Type is itself another object that's joined to the record via the RecordTypeId lookup field.