Some are suffering long delays to get into the game, others report countless small hold-ups during play and the disappearance of interactive parts of the Warcraft world. Intermittent server crashes have thrown players out of the game at key moments. To answer criticism, WoW maker Blizzard has posted a long explanation of how it is tackling the glitches.

"It's extremely, extremely frustrating."

Since it launched in November 2004, World of Warcraft has proved hugely popular and now boasts more than six million regular players around the globe. The game lets players control different sorts of characters, including warriors, warlocks, wizards, druids and rogues and take them adventuring in the fantasy world of Azeroth. However, some fear that this growth has come at a high price and the playability of the game is suffering as Blizzard struggles to support those millions of players.

Greg Lastowka, a regular WoW player and an assistant professor of law at Rutgers University in New Jersey, said in the most extreme cases huge queues had formed to get into the Warcraft game world.

In one example, some members of the same guild as Mr Lastowka were attending a conference together and arranged to play WoW via computers and a 50-inch plasma screen at a local research lab. "It sounds great, but the person with the plasma set got the pleasure of staring at the log-in screen for an hour, waiting for the server to authenticate," he said. "It's extremely, extremely frustrating."

The login delays can be particularly bad for players that control high level characters trying to complete some of the big dungeon areas in WoW. These feature tough monsters, valuable treasure and take hours to play through. Gathering enough players together to sack these dungeons takes huge amounts of organization - the biggest areas demand contributions from up to 40 people.

Lastowka said his guild scheduled dungeon raids a week in advance but all the planning often came to naught because of the stability problems. One player said these delays were particularly bad at battlegrounds where players take each other on in huge brawls, BBC News reported. The delays meant people often waited hours to be in the game for only a few minutes, said the player who uses the nickname Naunet in WoW.

Population boom

Jeff Woleslagle, a keen WoW player and editor at online game news site Ten Ton Hammer, said the over-loading could cause all kinds of strange errors when players got in the game.
Often, he said, loot grabbed from dead monsters took seconds to transfer from the corpse to the backpack carried by characters.

Others have complained of "layer peeling" in which players find themselves in an empty world as delays strip out the interactive elements of the game - such as monsters, computer-controlled characters and gatherable resources - which are not refreshed as characters explore.
These tiny delays often occurred at the most inconvenient times, said Woleslagle. For instance, he said, they could mean that healing spells were not cast in time and player-controlled characters got overwhelmed by foes.
"It's no secret that Blizzard's a victim of its own success," he said adding that the game maker was "tight-lipped to the point of creepy" about the problems.

Woleslagle said some of the problems were caused by poor management of the numbers of players on each server - each one of which is a copy of the Warcraft world.

To answer the ongoing complaints, Shane Dabiri, lead producer on the World of Warcraft development team, posted a lengthy document to the game's official forums on 3 May.
In it he said Blizzard was "not happy" with the performance of the game's 336 realms in the US and Europe. Each realm is a copy of the Warcraft game world.

He said Blizzard was adding 22 realms in North America and 30 in Europe to help manage growth. Also ongoing were upgrades to hardware and software to support existing copies of the world. Blizzard also planned to start a migration scheme which would let players, for a fee, move to another server so they can adventure with their friends.

Finally, he said, Blizzard was moving to improve the log-in system to reduce delays. He said a new authentication system was being rolled out that should be in place in the US and Europe by the end of May.

Mr Dabiri wrote: "We feel it's unacceptable when even one player can't enter the game, gets unexpectedly disconnected at a key moment, or experiences any other interruptions while playing."