@Simon B If it works on the Mac then it should work on a PC.
Check how you are creating styles within your source code. This is where the error is being reported.
Also, as Dave said above, you need to be running an Excel version that can read the XML format. As far as I can remember the format is Excel 2004 but don't quote me on that!
Yeah, You were right. I probed the code, and the error happens when I try to Style the Cells.
Where 10 = the Column Number
i= the row Number, I plus 4 to start to write in the fourth row.
And "Moneda" is the name of the Style declared at the beginning of code:
xl.StyleHorizontal = xlAlignRight
xl.StyleNumberFormat = "#,##0.00_ ;[Red]-#,##0.00 "