If you are having problems saving files, it is most likely that you have run out of Disk Quota.
You should Check your quota, and probably clean up some files.
If you are still over your quota, even after cleaning up your files, there could be a number of reasons:
There are files owned by you somewhere other than in your home directory (or /tmp), eg. in a directory belonging to another user whose group you are in. Such groups are frequently used for group assignments in some subjects.
Your .Xauthority file does not have write permission set, which the system interprets as meaning "I can't write to this account, so it must be over quota".