Did you follow all the instructions listed here?:

https://aximmetry.com/learn/tutorials/for-aximmetry-de-users/how-to-install-third-party-code-plugins-for-unreal-editor-for-aximmetry/

Hi, thank you  for your reply.
I followed all steps and installed "Prerequisites" by installing SDK's Librairies and all steps.
And tried 2 plugin installation methods (Manual and Automatic by bridge app) it works on Unreal engine Original by not in UE for Aximmetry.

Please can you give a hand ?

I got same error message

Finally it worked. thanks to aximmetry support.
All you have to do is to install plugin via Bridge installer on Unreal engine Original.

Make sur to install Unreal For Aximmetry in same version as original.

Open UE for aximmetry 

click aximmetry in menu bare then install plugins

then click on plugins, Find megascans then enable it.

Restart and BOOM!
Thank you