I had a problem like this, I decreased the sensitivity in all metal mode and it helped. Note that when switching between programs you will be switching to that programs sensitivity settings, so you will have to adjust it again. I tend to leave mine at about 50. If you are trying to pinpoint a very deep target, this setting may be too low, so you may need to bump it up in that case. I don't really get targets below 5 inches so this setting works for me universally. (Whites says that a lower AM sens mode will also help to reduce falsing in search mode, for some reason.)
Another potential solution is to go into the expert menu and turn ratchet "on". This helps the vision to take a big signal, which could overload the machine and make pinpointing difficult, and essentially shrinks the signal.
Probably the easiest solution if it is a near-surface target that is large enough to be causing some overload, but your settings are working for you for most of your hunt that day, is to lift the coil a few inches above the ground to pinpoint. This may decrease the "size" of the signal that the detector sees coming back from the target, allowing it to pinpoint without overloading.
What is your current all metal discrimination setting?
The village idiot,
Nugget