One of our list had all of it's juno subscribers deleted.  Any idea what this error means?

The following 10 subscribers were deleted from the ***** list today:

...
  *****@JUNO.COM
  Last error was: 5.2.0 550
                  57a4edc1019d89a4dd81604d444d813d4d4d1090b1fdd059c9d19931d089a
                  9a431a924948d80c10500d5a14dd90480f10d0184
--
If a word in the dictionary were mispelled, how would we know?

Bill Verity - 814-865-4758  Fax: 814-863-7049
215A Computer Building - Information Technology Services, Penn State University
At the office - on my Mac, of course ;-)