How I've always interpreted this rule is that once you are completely blocked - IE none of your pieces can move because primes are built in front of all of your pieces, and they are all immediately behind said primes, your opponent must move a piece. I've never had a problem with this before, but my current opponent has a slightly different interpretation, and when the rule is read literally, I can understand their viewpoint. They are suggesting that all of my pieces must be on the same point, since the rule says: "if opponent has collected all his checkers onto the one point behind player's prime". Now, that seems to me like a strange rule, as it would be extremely rare to be blocked in only one place, but that is what it says. So, who's right? Here's the game in question:

If that link doesn't work, you should be able to find it in my Started Games, me vs. ekko. You'll notice that I have a single piece stuck behind my opponent's prime (11 rolls in a row with no 6 - argh!), and then my other 14 pieces on one point that is behind what is effectively a two-point prime. I believe the intent of the rule would be that this fits the criteria, but I can see that the rule isn't worded in quite that way.