Batch VB stops when other apps accessed

I have a directory containing several .csv files that contain lists of stock symbols. I have an Excel workbook with a macro to read all of these .csv files and update a workbook in another directory named for each stock symbol. When I run the macro all by itself it runs fine. When I run the macro and then move to another application like Outlook or IE or Windows Messenger, the macro eventually stops executing. At that time the workbook for the stock symbol it was working on is displayed, with the .csv workbook in the background plus the original workbook. How can I make this a multitasking operation so that while my macro is executing I can do other things on my computer? I tried Application.Interactive = False but still had the same problem.