I ran into a an issue today. When I tried to add a user to a site in my SharePoint 2013 site, I got this error:
Sorry, we’re having trouble reaching the server
A google search gave these two possible solutions:
I know it can almost everything that can cause this error. Here are my two öre 
I found that when I tried to add a user, an ajax call was made. And this was the error:
The Web application at http://10.10.10.151 could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application.
Obviosly, the Alternate Access Mappings. What I needed to do was to add the ip-address to my AAM.
