If your Windows username contains characters outside of the alphabet or numbers one-to-10 then you may run into issues playing Grand Theft Auto 5 on PC.
A fix is currently being worked on, Rockstar said, but until it's ready you may have troubles connecting to the update service.
You can either wait or you can make a new Windows Administrator User Account without any special characters to tackle the issue. There's a guide on how to do this on Rockstar's site.
The Steam store page for GTA 5 highlights the same issue.
Some people do have the game up and running, and have recorded GTA 5 PC running at max settings in order to make everyone else feel jealous.