the problem of dle, dll etc... plugin is the framework version, max 2011 use framework3.5 and max9 use 2.0.
When you build a script do it with .ms format in max9 (is a script not a plugin) so will be compatible for all max version, if you want encrypt your script use the .mse format.
Why build a plugin or a encrypt format ? with this behavior is not possible to publish the source code and when the creator disappear we loses all his work.