My son has been a DREAM... until he turned 9 mos. Each nap, it would usually take less than a minute to put him down. (Naps 8:45ish - 10am and 1:30ish - 2:45) But recently, he has been screaming as soon as he sees that I'm walking him to his room, and especially when I lay him in his crib. Where did my sweetie pie go?
So I've simply let him cry. he eventually falls asleep, but on one day he cried for more than 45 minutes which is extremely unusual. I picked him up a few times (didn't talk to him) and immediately, he started laughing in my arms! What a sly boy!
I think it is seperation anxiety, and also at this stage, he seems extremely aware of everything.
If you can handle it, put your LO down when it's the right time, and even if they cry and wail, you have to show them who's boss. (i know that sounds mean, but it's worked for me)
Today, he cried about 2-3 minutes before falling asleep for his AM nap.