Regarding 'invalid argument: b must have a dense head'

Hello, I have a database that I've been using for a while and which is updated several times a day. Recently when trying to insert records, there is an error: GDK reported error: BATsubselect: invalid argument: b must have a dense head. Could someone explain what this means, and how/if there is a way to fix the problem? The command that produces the error is quite simple: INSERT INTO sometable VALUES (blah,blah,blah...); and since it's part of an automated process I don't think anything has changed. It was successful up to a two days ago. Thanks! Tim