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>I have set UpdateName to "" for concatenated fields with no problem as long as Updatable property is false. Otherwise, I use the correct UpdateName but still set the Updatable property to false.

I think you are right, that is the distinction. If the field is computed in some way so that there is no single database!table.field source for a field, we can use "". If there is such a single database!table.field source, the field updatename property must be set to contain it, regardless of whether the field itself is updateable. Thank you again.