The ExportFieldValue.aspx page and associate code-behind file has been updated to enable exporting data with scaled images and limited text in conjunction with Ajax-enabled pop-ups.
During migration, the ExportFieldValue.aspx page and ExportFieldValue.ascx.cs and .vb code-behind files in your application are replaced with updated files. Any changes you have made to these files will be lost, though it is quite rare for developers to customize these files.
After migration, re-apply any changes you may have made to the original ExportFieldValue.aspx page and ExportFieldValue.ascx.cs and .vb code-behind files to the new files in your application.
Version 4.2 Application Migration