Creating app for Excel 2003 with Excel 2007

I'm writing .Net desktop application to create reports in Excel 2003, but I have only Excel 2007, and have no license of Excel 2003. This is my problem, because when I launch this app on client’s 开发者_Go百科computer (Excel 2003), I have error (SystemNullReferenceException).

I know reasons of this exception (different versions of Excel), but I don't know any solution.

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Not sure whether it will work but you can consider installing excel viewer on the client's computer. It appears to be a free download of about 75 MB.