Is it just me? About 25% of the time I book on co.com, I am unable to select a seat. Since I commute on Continental every week, it's very frustrating. I book 2+ weeks out, so that's not the issue - the seatmaps are often wide open. I also lost both seat assignments on my flights next week.

That's a new one on me. If you book two weeks out, I just don't know why you can't get a seat. Can you call CO and get a seat assigned that way?

The original poster (OP) stated both an inability to 'select a seat' as well as 'lost ...seat'. I am left with the impression that they were not prevented from obtaining a specific seat assignment when they booked, but instead have found that the inability 'to select' is essentially equated by the fact that they are finding that they are losing their seat to someone else after having previously chosen it.

This recently occurred to me on an international leg (IAH -> CDG) with my business-first (BF) seat reassigned without any notification whatsoever. I just happened to review my itinerary. As others have responded on that thread, this can occur if there is a change of aircraft (sometimes same type of aircraft, but different layout) or a flying air marshal (FAM) is subsequently assigned your seat. I imagine there are other reasons for this to occur, as well, but the aforementioned seem the most likely candidates from what I have read.

Both - sometimes I cannot select a seat and get this:

! We were unable to assign some or all of your seats. An agent will assist you at check-in.

And new this week, I lost my previously selected seats (in Y).

Unable to select seats is something that happens from time to time. CO stops allowing people to select seats based on load at some pre-defined level (50%-75% of seats assigned, based on the route). They do this to allow for sufficient flexibility in seat assignments in the airport for people who need to move around.

Not sure about losing seats (especially in Y since is wasn't a FAM), but it is known to happen that some people manage to convince a CSR to move the sets around.

This happened to me last week when I booked a flight from EWR to ORD. There was 5 seat left and I could not choose a seat on online. When I called the agent assigned a seat for me.

Thanks - this explains a lot. 50% seems a bit excessive...and is quite frustrating.

I sure wish the agents would take advantage of this and stop telling people that the FAs will get them their seats together.