Abhimanu,
Sorry that you are seeing this issue.
As a workaround, you can try the Dropins method to install the plugin. Shutdown MyEclipse 8.x.
Extract the downloaded archived zip file, copy the plugins and features folders to the dropins folder of the MyEclipse 8.5 installation directory. If you already have plugins and features folders created in the dropins folder, then just copy all the contents from the plugins folder and the features folder of the extracted zip file into the plugins and features folder of the dropins folder. Restart MyEclipse 8.5 and you will see a prompt about the plugin being installed successfully.
Please note that versions earlier than MyEclipse 2016 are no longer fully supported. We try and assist licensed users working with older releases but no fixes will be made to those releases.
MyEclipse 8.x is quite an old release and is not a stable one. The MyEclipse Configuration Center is also discontinued so you might see problems installing plugins from the Configuration Center. The newer versions of MyEclipse support latest tooling in the development space including Angular and TypeScript and it has significant performance upgrades as well. I strongly recommend you update to the latest MyEclipse 2017 version. The license you currently hold is valid for the latest releases as well.
You can download the latest 2017 installer from here : https://www.genuitec.com/products/myeclipse/download/
Install 2017 alongside your existing MyEclipse 8.5 release to a different location and give it a try.
Hope this helps. Please let us know how it works for you.
–Swapna
MyEclipse Support