Your account is most likely over its disk quota, and your X-window session cannot write any files into your home directory.
To fix:
Log into the system via the console (press CTRL-ALT-F2)
ssh to bohr.
Type the command 'quota -v'.
Find the files that are using all your space with the 'du' command. (type 'man du' for information on usage)
Remove, move away, or compress files such that you are below your quota.
You can switch back to the X-Window login by pressing CTRL-ALT-F7
Remember to logout of your console session when done with it for security reasons