Whenever you login, by default, the quota of your locker is checked (and any other lockers that are attached to which you have write permission), to verify that you (or the lockers) are safely under quota.
If you are close to your disk quota, you will see a message such as this one during the login process:
If you are over your disk quota, you may see some popup dialog windows with complicated-looking error messages. Unfortunately, these error messages are not useful in and of themselves, but they indicate that some programs are not able to write files that they'd like to because there is no free space.
If you are over quota or close to your quota, you should IMMEDIATELY take action to reduce the amount of space you are using, or you may not be able to save any new files to your account.
N.B. If you receive a quota message about a locker other than your own (for example, a group locker), you should still take action, but it will not affect your ability to log in or any files stored in your own locker.
For more information, see the following answers in this category: