Can't pick up 'Archive Tower Giant Cell Key' to free Logan

When I try to pick it up, it appears on the ground as if you have max out of one item and try to pick up another..

I'm uncertain on how to solve this.. or if it is even possible

If anyone has had the same problem or something similar, please post what you did to solve it.

Thanks in advance,
Eilith~

I get this problem with the enemies in the room with the anor londo painting. I think they're meant to drop their knives but it doesn't let me pick them up.

You probably already did this, but did you try restarting the game?

Also, he will free himself after you defeat Seath the Scaleless. He will appear where he usually does and sell his stuff.