There are so many low points, that it's difficult to single one out....the 2001 FA Cup final was a low point, because we'd been without trophy since 1998 - if I'd known back then that we were going nine years without silverware just four years later, I wouldn't have believed it.
However, the 2002/03 season was a huge let down as well. The whole Invincible era was a let down in terms of "silverware-output".
The CL Final...well, I'm yet to see anything of that game again, as I still refuse to ever watch it again. I felt we're robbed that day, and it'll hunt me for as long as we don't win that damn trophy.
After that era, the 2008 and 2011 breakdowns stand out for me, as the two lowpoints.