I have an append query which, until a few hours ago, ran fine. Now when I attempt to run it, it always fails with a message saying that the records which should have been added were not, due to validation rule violations. However, the table that's being appended to has NO validation rules whatsoever (either at the record or field level). Also, when I display the result of the append query (by going first into design view and then switching to datasheet view) and then manually copy each field from there into the target table, it works fine. All this began when I added two new fields to be appended, but now even removing them does not cure the problem. Any ideas?

You probably need to change the "allow zero length" property to yes for fields that are not required.

Thank you, Pat! That was the magic bullet I needed.