I've been getting this when I have a lot of pictures up on my profile. If I delete some of the old ones, then I no longer get the error...
Perhaps there is a quota assigned to each user? If so that should be stated explicitly, or better error handling if/when the user surpasses the quota. Also, for paying members, the quota should be much higher (or non-existent, as space is cheap)...
My two cents :-)