I notice that both of you are on Macs. Did you update Quicktime to 7.15? If so, I've seen it wreak havoc on library manager. I've heard that you have to manually downgrade to Quicktime 7.13. Also, check all the permissions on your folder. I was having this problem too on Mac OSX 10.3.9. I spent 3 hours on the phone to Graphisoft and they were stumped. The operating system had to be reinstalled to get the problem to go away. I tried reinstalling Archicad, trying each different build, but it ultimately came down to the OS.