Problem outputting large sheets (Excel 2007)

When i try to output a large Excel 2007 sheet (over 695 columns), Excel says the file contains unreadable content. This only happens when there are lots of columns. The interesting part is that nothing is lost, but Excel inserts
extra columns that are completely empty (and were not part of the
output). Scroll to column AYZ of the attached file to see this behavior. Same thing happens when i do not use merge cells. I can provide more file samples.

Here is what Excel says:

Excel found unreadable content in ‘test.xlsx’. Do you want to recover the contents of this workbook?

Then it says:
Excel was able to open the file by repairing or removing the unreadable content.
Removed Records: Cell information from /xl/worksheets/sheet1.xml part
Removed Records: Merge cells from /xl/worksheets/sheet1.xml part

I have attached a sample output file, which i saved using method…



Please try the attached version.

Thank you.