[harryh]

There is ample precedent for forgetfulness in the courts. Imagine a scenario where you are called as a witness in a case against someone else and you say that you can't remember what you saw. If there is evidence to support the idea that you are lying (say, you're being asked an easy question about something that happened yesterday) you can be held in contempt.

If there is reason to believe that you are telling the truth (say, you're being asked which of two parking spaces you saw a car in 10 years ago) then you're fine.

Same thing goes here. Rational disinterested people (a judge or a jury) will look at the available evidence and make their best judgement about whether you are telling the truth when you say you can't remember.