This is a known issue with certain computers, and it will be fixed in a new release of the AMPL IDE soon. As a workaround for now, you can create an empty text file, for example by using File/New in Windows Notepad; then save your empty file and open it for editing in the AMPL IDE, where you can type in the contents. In that way you do not actually have to create the file in the IDE. Since most of the time in model development is spent editing files rather than creating new files, this extra step should not add much to your work.
Bob Fourer
am...@googlegroups.com