Odd. Just a few question to see where the problem could be:
-when I select an empty folder as Blender’s scripts location in Blender’s user preferences, I don’t get any error messages. What is the exact error message you’re getting, and where does it show up?
-have you located Blender’s scripts folder? If so, where is it? Does it contain any files, like 3ds_export.py? If not, can you locate 3ds_export.py on your computer?
-what is the exact path to the folder where you put the scripts?
-after setting the path to the folder where you put the exporters, have you saved your preferences?
-if you open an exporter file in Blender’s text editor window and press alt-p, does the script run?