I believe if you open a file for write access without the Append parameter, it just overwrites the old file. In other words, there should be no reason for deleting the old file first.
I don't use read/write that often. Is the permission problem an operating system problem or is it an excel issue? If it's excel, it may be that you're opening the file for read access then trying to write to it in that mode, which won't work. If you need to open the file to find out what the serial number is, do so, then close it and open it in write mode (with no Append parameter).
Hope that helps :)
Last edited by mtranchi; May 17th, 2011 at 10:46 PM..