Firstly, ensure that selected plug-in has compatible with your EDIUS has been installed. Confirm plug-in maker’s web site more details

Also, ensure that you run plug-in installer after finishing EDIUS installation.

Both of above are no problem. Try to re-install EDIUS in order to rebuilding effect tree.

NOTE: Sign into the OS with administrator privileges

1) From Apps & features, uninstall EDIUS. Untick ‘Deactovate the license’ while uninstallation 

2) From Apps & features, uninstall the plug-in. If you install multiple plug-ins, uninstall all of them

3) Delete C:\ProgramData\Grass Valley\EDIUS folder

4) Delete C:\Users\{USER NAME}\AppData\Roaming\Grass Valley\EDIUS folder

5) Restart the OS

6) Install EDIUS

7) Install the plug-in(s)

Install latest build
If currently installed build is not latest one, install latest build. To do it, follow below steps at step#1

1) From Apps & features, uninstall EDIUS, Mync  and GV License Manager. Untick ‘Deactovate the license’ while uninstallation.

2) Download the latest build. Use the installer at step#6