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You have attempted to use a field name that is already in use on the dataform - this . This could be a system generated field, such as CreateDate, UpdateDate, CreatedByUserID, UpdatedByUserID, etc. .. SQL will not allow you to create two columns on the same table with exactly the same name, hence the error.
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Change the field name and re-save. Avoid using any of the names for the existing fields on the dataform, or any of the system protected fields. If you are unsure of the pre-existing field names, you should run the "Dataform Specification" report to get a list of all the current dataform field names.
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