From my research (given what's available is certainly less than fact) Project Looking Glass is a projection of the future based future that person wants to see. It's like a collidoscope, you can see all possible timelines and then focus on one specific one based on current events or events you are planning. if the timeline you want doesn't exist at the point in time you are trying to see you are simply taken to the end of that timelines existence and no further.

Additionally, the projections have to be channelled through a spiritual intermediary which adds an element of error or mis-interpretation. Current information suggests that the Project Looking Glass didn't fail so much as it didn't show the cabal any of the future timelines they wanted to see past certain dates. That's why they stopped using it because it was the mirror on the wall, it told the truth which made it the enemy.