“Compatibility mode” isn’t really as compatible as the name implies. Formulas are generally okay; formatting usually has issues; shapes, charts, and worksheet controls usually behave strangely; and structural workbook things like headers and footers are a crap shoot.

I’m not sure using the converters in old versions of Excel helps that much, but you might try it on a copy of your file.

2. This Workbook was transferred into Excel Office 2010 and opened in the “Compatibility Mode”
2.1. The Chart in Sheet 2 was adjusted to fit a Lansdscape A4 print configuration.
2.2. The “Print Titles” corner arrow in the Page Layout – Page setup group was selected revealing the Header and Footer Tab
2.3. A Title and Info in all three sections of the Custom Header was entered.

3. Print View was chosen and all the information appeared and printed out successfully.

4. On performing any moving or manipulation of legends etc or saving the document , the Print View failed to show the Header information – nor did it appear in the printed document.

5. On Sliding the chart into the page area below it, the header data re-appeared in the Print View.

6. This remained so when the Chart was put back in position and all printed satisfactorily.

7. However after saving and closing, on re-opening the Header had disappeared again.

8. I manipulated the chart position as at points 5 and 6 above and the Header re-appeared etc.

9. The only way I found to solve this was to take the workbook back to Excel 2000 and enter the Header details there and saved it.

10. On re-opening in Excel 2010 the Header appeared and remained!

11. Is there a better solution?

12. I did not try converting to *.xlsx to see if this avoided the problem as I needed to keep it operating in *.xls -perhaps I should by using the converter facility available for earlier versions of excel.

You can do this for any function. You could try the LOGEST function in place of LINEST, or you could transform your data first, then use LINEST on the transformed data. I’ve read about issues with the calculation of sums of squares and errors with transformed data, but I’m not sure where to suggest you find further information.

Check out Error 3 in Trendline Fitting Errors. Then check out the other errors just to be safe.