We should never take these reports that IB had prior information about a particular terror attack and they had warned about it before hand, seriously.
These are not my words but the words of TN Sheshan who knows better as he was also a Security chief of Rajiv Gandhi.
According to TN Sheshan, IB files a routine reports like this. If nothing happens nobody bothers. But if something happens they claim that they had prior information and they had warned.
They just do things to save themselves from the blame.