Manually created Excel files (in BIFF8) cannot be opened in Office 2007/2010 on Windows 7

We have a program that manually creates Excel files in BIFF8 format. This is a server program that runs on UNIX as well, so it doesn't use any COM library, but writes the file binary data itself.

It is used to work very well, but the files it generates can no longer be opened in Excel 2007 or 2010 when running in Windows 7 - Excel says the file is corrupted, but Open and Repair doesn't work as well, and the file is not opened.

When in Windows XP, the files can be opened in Excel 2007 with no problem.

Can you think of a reason for it not to work in Windows 7, or any possible workaround?

(We would like the program to be able to create files that can be 开发者_StackOverflowopened by various Excel versions, and not to create separate BIFF8 and BIFF12 files)

I have found that OpenOffice/LibreOffice will often open Excel files that Excel itself won't. If you then save the file it may be possible to open it in Office 2007/2010. You can even automate this process, though that's a bit fiddly.