.xls file not opening in the Windows 7

Hi,

I have a VB.NET (VS2005) application that creates .xls files using the Interop.Excel version 1.5. The file is created and opened succesfully from the application. But when trying to open the manually from the folder it was copied to, it gives an inavlid format error.

We can't change the reference of the excel to the new one since there are some machines which still use windows xp. how do i accomodate this keeping in mind that some of the machines are xp and some of them are window 7. Can the VB.NET application have both new and old excel object reference.

Thanks

Padma