I don't know if it has anything to do with what 
happened to you, but I'll paste it anyway:

  "Don’t let your account freeze up! 

  Did you know that if your account goes over the 
2MB storage limit, it will automatically be 
frozen? That
  means: 
   You won’t be able to send any messages 
   All e-mails sent to you will bounce back 
without notification 

  Your account will stay frozen until you delete 
enough e-mail to put you under the 2MB limit. 
Then, you'll
  need to keep monitoring it to make sure you stay 
well under the limit. 

  The better option is to sign up for MSN® Extra 
Storage. For only $19.95* per year (less than $2 a
  month) MSN Extra Storage gives you 10MB of 
storage — five times what you’re getting today. 
It's the
  easiest way to avoid a frozen account."