If you are doing Excel Automation, and are having errors like "Exception from HRESULT: 0x800A03EC" or "Old format or invalid type library" probably it’s a location problem.
One solution is to force a culture change when using excel objects, but there’s a better and simplified way, that only requires to instantiate the Excel.Application object like this:
Excel.Application excelApp = (Excel.Application)Microsoft.Office.Tools.Excel.ExcelLocale1033Proxy.Wrap(typeof(Excel.Application), new Excel.Application());
With this all the comunication with excel via this object will be done in locale 1033, it basically creates a proxy that comunicate with Excel always in locale 1033 like in VBA.
For more detail check: