If Notepad++ isn’t running, COM will start it automatically. Unfortunately COM appends always an “-Embedding” to the command line.
So Notepad++ will be started like:
“C:\Program Files(x86)\Notepad++\notepad++.exe” -Embedding
This causes Notepad++ trying to open a non-existing file called “-Embedding” at program start, which is very nasty and prevents the ActiveX plugin to do its further stuff.

My feature request is, if you please could ignore the “-Embedding” program line argument, if specified.
I forgot this topic somehow but someone has created a ticket now for my plugin and that topic:
https://sourceforge.net/p/nppactivexplugin/tickets/1/

Kind Regards
David Gausmann