>Playing around with the camera and SB800 just now, I realized >that the FP appeared after TTl in the flash LCD because under >Custom Settings>Flash/Bracket the maximum flash speed was >set to 1/320. I dropped it down to 1/100 and now the modes on >the flash appear as — TTl, TTl-BL, A, AA, M. > >Life has returned to normal.
Not quite 'normal'. You have also reduced your flash sync speed, so you will have to use a much slower shutter speed when shooting flash. This can lead to excessive ghosting. 1/250th is normally the best flash sync speed to leave the camera set to.
The reason you saw FP in the flash display was because the flash was set in Auto High Speed Sync mode. In that mode, when you choose 1/250th FP, or 1/320th FP,the flash will sync with speeds higher than regular sync speed. However, it also reduces the maximum flash power to less than 1/2 of what it is in regular sync mode.
When first learning the flash, I recommend that you turn Auto FP High Sync mode OFF in custom settings menu e1. Then FP will never appear in the flash display, and you will always have full flash power available.