Can't add keyframes

[Amie]

Hello.

I can add keyframes a couple of times to an object, but then I want to add another one to have it fade out, and it won't let me. 

My (light) object should start at 0% opacity. Then fade into 100% opacity. 

Then fade out again after a second or two. 

I can get it to fade in, but when I want it to fade out, it won't let me add another keyframe. 

Same with the "comesee" layer below, I can't even get that one to fade in from 0 to 100.

I've done it before with other files, and have tried starting from scratch, restarting, but nothing works. 

What gives?

Also, occasionally, it won't let me apply easing between certain keyframes. As far as I can tell, they're no different than other ones I have easing applied to. Any ideas?

Thanks!

Amie