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 next week – rest assured we’ll be monitoring and actively doing all we can to smooth such things out as they happen, but we need your help to find them, as well as your feedback to help fine tune all of the game's systems so everything is perfectly balanced.
One of the root causes of virtually every multiplayer mode's technical difficulties has been too many people trying get in at once. Square Enix wasn't prepared for "FF14" because, and they actually said this, the game had been so bad prior to the update that they assumed most players would let their hardcore friends play first and make the call later.
We still have no real plausible reason for EA's failure from earlier in the year. Anyhow, given how Rockstar has sold million and billions and zillions of copies of "GTA V", technical difficulties are going to happen, period, end of story.