lucy24 - 12:52 am on Dec 19, 2012 (gmt 0)
A WMT warning doesn't necessarily mean you did something wrong. It can be interpreted as "Did you do this on purpose?"
Do the pages currently exist? (Formally: Do the URLs correspond to physical pages that are accessible in some way other than redirection?)
If they no longer exist, did they formerly exist? If so, that's 410 rather than 404.
If they still exist, are they accessible to some people under some circumstances? If so, that may be 401 rather than 403.
What does "internal reference" mean?