In this section, I will try to provide some very basic diagnostic areas I would look at to fix issues in specific parts of the system.
If the internal network is working fine and people can connect to the Internet, but others cannot connect into your system, I would first check the firewall and router. Assuming that the basic connectivity checks are all OK, I would start with the Fix my network option in the Windows SBS Console under Network. Click on Next to start the wizard off and wait a few minutes as it can take some time to run.
Once the wizard has run, it will show you the issues it finds. If your router is not a UPnP router, you will always get a top issue of Could not configure the router. This can be ignored in this case, but other issues need further investigation. Some issues do not have a full description and the only way to understand the problem further is to type the link into a browser to find out more. Clicking on Next will...