I use a web-based application that generates CSV files. When I open
these from Internet Explorer they are automatically loaded into Excel
(2003). However after a few minutes I always get an auto save error.
The reason is that the filename created by IE will include something
such as [1].csv at the end of the filename. Excel does not consider
these valid characters and so gives an error when it attempts to
autosave (but oddly, obviously can open files with such a name OK).

It seems odd to me that IE creates a filename that Excel says is
invalid. Is there a solution to this (other than disabling autosave in
Excel)?