Is the Excel 2007 on the same machine as the Excel 2010?
If so, you might have some special issues due to this.
Do you mean the ribbon part of the add-in?
If so, you need to take some care with the namespace directive in the customUI xml section.
Otherwise, I suggest you take the simplest example from the Excel-DNA distribution (just double-click on the Distribution\ExcelDna.xll file). This should load and make available the =AddThem(..) function. If this does not work, either
- you saw no error or message at all. Probably then the security settings are preventing add-ins from loading.
- or you saw a message, which should give us a clue.
Once you have the basic Excel-DNA add-in working on the Excel 2007, and your add-in still does not, we need to consider what might be a problem with your add-in.
Do you even see the 'Registering ...." message in the status bar of Excel when you File->Open your .xll file?