Como "Copiar para nova planilha" não encontrou erros específicos, o problema provavelmente não é muito localizado.
Um possível motivo de Como corrigir / eliminar erros de PERDA DE FIDELIDADE :
The "loss of fidelity" is likely the result of different color definitions used between the two versions. If you want to save the workbook in the older format, you need to use only colors that are defined in the older versions of Excel. To see these, click on the Office button, pick Excel Options from the bottom of the frame, and go to the Save tab. Click on the Colors... button, and you'll see the palate available for the older versions. You can see the RGB values for colors in the palate by choosing one, clicking the Modify... button, and then going to the Custom tab. To avoid the annoying "loss of fidelity" message, you have to use colors with exactly the same RGB values for the colors in that palate. Check fonts, fills, and lines on all sheets in the workbook.