Cannot/could not

Should we say "I CANNOT remember when I last saw him?" or "I COULD NOT remember when I last saw him?"? Is there any difference between the two?

This is an R Berg question. Maybe: "cannot" is in the present. And "could not" the past?

Yes, that's the difference between them.

"Right now I cannot remember when I last saw him."

"Yesterday I could not remember when I had last seen him."

I really don't believe I'm the only one who could answer that question.

You're really right.