GTA Online players who haven't visited in the past year will have to wait for a fix from Rockstar.
Update: Rockstar updated its support post to note the problem is resolved. Some PS4 users were experiencing difficulties downloading a patch Rockstar released yesterday, but Sony increased the number of servers the patch can be downloaded from, which fixed the issue. All character migrations to PS4 and Xbox One are now working, and GTA Online is up as normal on PS3 and Xbox 360 as well.
Original story: This morning Rockstar Games responded to players who have encountered an issue that prevents transferring GTA Online character progress to PS4 and Xbox One. The company stated this issue only seems to affect people who have not logged in to GTA Online since 2013.
"No previous Grand Theft Auto Online data is associated with your Social Club account," an error message will state for those who have not logged in since 2013. When starting GTA Online on PS3 or Xbox 360, a different error message will state Rockstar services are unavailable.
Rockstar is urgently looking for a fix. The company suggested those affected subscribe for an automatic email notification when there is more information.
The PS4 and Xbox One versions of Grand Theft Auto V will have new vehicles, weapons, missions, and more. Rockstar is adding multiplayer heist missions to GTA Online, and server player count is increased to 30 players.
For people who have played GTA Online more recently, to transfer data you will need a Rockstar Social Club account. Any money you've purchased will not transfer outside of the same console family. For example, money bought for the PS3 version will not transfer over to the Xbox One version, but it will transfer to the PS4 version. Even after transferring, you can still play the old character on PS3/Xbox 360, but new stats will not transfer over again.
Grand Theft Auto V's PS4 and Xbox One versions released today, and the PC version will be available on Jan. 27, 2015.
Source: Rockstar Games