Most likely there is no error. What happens is that Excel NEVER opens multiple instances when opening a file. All the files are opened in the same process, with extra taskbar icons but a single window. So if you first instanciate in code an Excel.Application object, and fail to quit it properly (no more EXCEL.EXE in running processes), the next file you open opens up within the same (invisible) instance. Just make sure you properly dispose of the object.
Set objXl = CreateObject("Excel.Application")
...
For Each wb In objXl.WorkBooks
wb.save
wb.Close
Next
objXl.Quit
Set objXl = Nothing
