Came across a situation today that has never happend to me before. I booked someone on my FF miles. Flights were MAN-AMS-MSP. Award flight has been ticketed for weeks - and yes I did confirm the ticketing had gone though.

When he went to check in at MAN, KLM refused to check him in for the AMS-MSP leg and told him he'd need to get to a transfer desk in AMS. His flight was late, he ran to a transfer desk, and they said the flight was totally full, his only chance was to hurry to the gate before the doors closed and see if he could get lucky.

He did end up getting the last seat on the flight. But I am puzzled as to why he couldn't check in for his AMS-MSP leg. I've flown MAN-AMS-MSP dozens of times and always checked through without an issue (I am PE, he has no status). Does KLM do this in an oversold situation, denying check in to certain pax? In the end it worked out, but I would have been upset had he been denied a seat.

Edit: I'm not suggesting any wrong-doing by KLM necessarily. But I fly quite a bit, and in my experience, people who lost their seats would be the ones who checked in last - and my friend tried to check in and was refused. That is what I find puzzling - all flights were ticketed by NW, and never before has KLM had an issue checking me in.