File is corrupted after applying conditional formatting
 

My Excel 2007 file works fine, I can applly some conditional formatting and
save it, then I can reopen it.
But if I run a macro that applies the same conditional formatting in many
ranges, everything works well, but after I save Excel is not able to open the
file. I get the message "Excel found unreadable content in...", and the file
opens without conditional formatting.
I think this is more a bug report than a question, but I don't know where to
report bugs.
Thanks,
Stefano