Is it the same program that asks for it each time you try to run it?
The "Unicode" version of ALT70.dll is intended for use on systems running Win2k/XP. The "ANSI" version of ALT70.dll is intended for use with Win95/98/Me.
The program asking for the file (if it's a valid Win9x compatible program) might have a copy you can use. If it's been overwritten with the Unicode version, uninstalling/reinstalling - or a repair install - of that program - might fix it.
. . . Gary