Recently, I was trying to connect to the trail version (9.0) using Plugin Registration Tool which was working some days back.
The reason for it was with Version 9.0, we have download all Tools, Dlls fron Nuget.
Here is the way to download the Plugin Registration Tool from nuget
1) Open Visual Studio
2) Create a new Project (Console Application)
2) Go to Tools -> NuGet Package Manager -> Manage NuGet packages for Solution.
3) Browse and install “Microsoft.CrmSdk.XrmTooling.PluginRegistrationTool” 188.8.131.52 version.
4) After installation, go to the project physical folder and open Packages folder.
5) You will see Plugin Registration Tool there and use that connect to CRM for registering plugins.