This error can occur when duplicate fields are selected to Export. To resolve remove one of the duplicate fields and attempt to export.

Note: Users have commonly reported this error when exporting the field Pledge Balance or when exporting two functionally equivalent fields outputting the same calculated value. For example, when outputting the field ‘Pledge Balance’ and ‘Gift Amount’ where the Gift criteria is set (checkbox) to calculate the pledge balance instead of gift amount when the gift type is a Pledge record.