The same problem on Ubuntu 14.04 x64
Same issue already reported in this issue: https://github.com/ValveSoftware/steam-for-linux/issues/3936 (more details available there).
Work-around is obviously to temporarily boot into prior kernel (-58) from the grub menu.
I had an update today via Ubuntu Software Updater. It updated kernel 3.13.0-58-generic to 3.13.0-59-generic. Steam client is normal but library have some issues. Steam says, "Available space is 0MB" but i have enough speca... Downgraded the kernel to 3.13.0-58-generic and it's ok again.
If you test and can not generate the error, i can update and generate it for you.