This is a Web patch file for tex.
The patch changes TeX such that, when it cannot find or write to a file in interactive mode, it saves the current file name before asking the user to input a new file name. It will restore (and use) that saved value when the net result of the user's input is empty.
Therefore, when the user just presses return, it will do another attempt on the file that failed initially instead of attempting to use an empty filename.
This patch is included in the upcoming TeX-Live 2004.
The change file