appears to be a common problem, I found this suggestion.
I had the stuck seat problem on my 2004 Buick Rainier and found a solution here on trailvoy but on another thread. I was looking for it and found this one so I thought I'd make this my first post It seems that the silver piece that goes between the track gets out of alignment and another poster on another thread suggested sliding a screwdriver under the silver rail, from the front, and lifting a bit to re-seat or release whatever is stuck. Well I tried it and it worked just fine! I just used a philips screwdriver, (the other thread suggested a flat tip screwdriver but it seems anything that will fit under the silver piece and allow you to lift it just a bit will work just fine), slipped the tip under the silver piece and pried up just a little and it started working! 10 seconds at the MOST.