You were trying to install ShortPoint on SharePoint Server 2013. And then the installation stops and show this error:

Error: Cannot add the specified assembly to global assembly cache: Newtonsoft.Json.dll.

Reason

During the installation, the process managing the installation was unable to deploy a required assembly [DLL] to the global assembly cache [GAC]. This happened because you have already the same dll file installed and our solution is trying to add newer version of the same dll.

Solution

Remove the dll manually and run the installation again by executing the following command:

gacutil –u Newtonsoft.Json.dll

Important: Best practices for successful installation