The update was pulled by Sony after a number of users reported problems with their consoles. It appears that some users were subject to blank screens when trying to play some games, including Metal Gear Solid 4 and system crashes.
This is what Sony has to say:
As has been reported on many gaming blogs and websites, we have temporarily taken Firmware v2.40 offline. We’ve received a limited number of calls from consumers experiencing an issue with installing the system software update on their PS3. While our consumer services department has seen a low volume of calls on this topic, we are committed to providing the PS3 community with XMB access features delivered in the v2.40 update. We are working diligently to isolate the problem for those few consumers and to identify a solution before we put the firmware back up.
A few users have replied to the comments on the official blog claiming that they have installed the firmware with no issues whatsoever, whereas other are complaining that it is full of bugs.
It's unclear whether users who have already have downloaded the patch,and have no problems, will need to re-install a new update when it arrives. We're expecting an official statement from Sony shortly.
Source :: Playstation Blog