Without seeing any code, it's virtually impossible for us to help. I can tell you that what you're experiencing is a common problem when trying to automate various versions of Microsoft Office with a single code base. Microsoft likes to make big changes in the APIs from version to version, some breaking changes. The first thing you need to do is identify where the code is failing. The easiest way to do that is debug the code on a machine with Office 2010. If that's not an option, the next thing to try is writing out debug information into a log file. Typically, a simple Try\Catch will work, then you take the Exception that you receive and examine the e.StackTrace. The StackTrace will generally tell you exactly which method failed.
Thanks Jason, I followed your advice and used my home computer with Excel 2010 to do the build. I did the original coding at home, but then transferred it to work to make some modifications. Seems to work now.
I'll try and figure out a way to do it properly when (if?) I get time.
HP Z420 16GB RAM Quadro K4000 ST7 MP10 on Windows 7 Pro 64.