It's because you're using the same entity via ElggGroup class.

You should extend this class in the custom plugin and then call your new entity.

There're other things to do but start with class extending.

Please learn Elgg docs (especially Related section there).

Elgg docs also has Copy a plugin FAQ.

There're same discussions about cloning group: 1, 2

They may be old but will give you some ideas of what to do.

I just want to say that the OP deserves a more complete answer than "Please learn Elgg docs ".  As someone who has spent many years studying and learning elgg, I find the documentation to be hard, sometimes impossible, to implement.  Such a statement is offensive and negatively affects one's attitude toward adoption of the elgg framework.  A (far) more helpful response would be to actually look at the code that Ahmed posted and recommend a correction that he can use.  Like, copy/paste use.  I would dearly like to see answers that are as thoughtful and helpful as what one might get at StackOverflow.com.  That should be our aspiration.

Short or long answers, with or without code, there are many types of answers. Community members are taking the time from their busy schedule and doing the best to give good and helpful  answers. We should be very grateful for every answer.

Look what Nikolai did in his above answer. First of all he gave a valid answer. Then he searched the Docs and gave the link. Then he made a general search and recommended a useful discussion and gave the link. All this takes time and you get it for free. And he have been answering many questions for long time.

Fortunately, there are more community members that answer questions. Usually, I get good answers, and feel uncomfortable that I can not return as much.

Anyway, thank you for your comment.  It gave me the opportunity to thank this good people :)

Same problem you've in your previous discussion.

You're trying to invoke entity 'group' with subtype 'school'.

But where did you create it in your code?

You just need to extend ElggGroup class.

Elgg will inform you about any conflicts.

Check your server's log also.

You may want to learn more:

http://learn.elgg.org/en/3.x/appendix/upgrade-notes/2.x-to-3.0.html

http://learn.elgg.org/en/3.x/guides/plugins.html

I hope you mean you installed the correct version for Elgg 3.3, which on the community is version 14.0.1. On Github we have version 15 available https://github.com/ColdTrick/profile_manager/releases

When enabled on the admin backend under Configure -> Utilities -> Edit profile fields you can manage the profile of users and groups.

Also there are some plugin settings.