When I send my .xls files from my Mac (Office 2008) to my boss's Windows machine (Office 2003), he gets an error message when he attempts to open the excel spreadsheet: Excel has encountered an error and must shut down. I've sent files to other computers and not had a problem, and my boss has received other excel files and been able to open them. So it must be something between these two machines/softwares that is affecting it. Any suggestions or ideas? I can add any additional info you need. Mac is running on Snow Leopard. Windows is running on (wait for it...) Vista.