No matter how well prepared a publisher might be, any online game (or simply a game that has online elements) is going to have difficulties at launch.
EA had them with "Sim City", Square Enix had some also with "A Real Reborn: Final Fantasy 14", and Rockstar will more than likely will as well the online component of "Grand Theft Auto 5".
Says who? Rockstar themselves.
Rockstar recently published a statement concerning the upcoming multiplayer service, which goes live on October 1, and they hope everyone exercises a little patience and understanding when the switch is flipped:
There will be the typical growing pains for an online game, including but not limited to crashes, glitches, crazy bugs, gameplay modes and mechanics that need re-balancing and other surprises! ... This sort of thing is inevitable in a massive open-world game and there’ll surely be lots more unexpected oddities like this in the Online world »
- Matthew Hawkins