What are some examples of reversible errors in the situation described below?As a general rule a different attorney is appointed to serve as the...

From the description that you have offered, I do not see
reversible error. It is not at all uncommon for separate counsel to represent indigent
defendants simply because that attorney may specialize in appellate practice. Trial
attorneys representing indigents are often quite busy and an appellate assignment might
well be unduly burdensome. A defendant who has retained his own counsel is by no means
obligated to continue with that counsel through appeal. He may retain appellate counsel
if he wishes, since he is responsible for the cost; or he may remain with his trial
counsel who is familiar with the case. It is not unusual for defendants to retain
separate counsel for appeals simply on the basis of the appellate attorney specializing
in that practice.

As far as the writ of habeas corpus that
you mention, I assume you mean allegations of ineffective assistance of counsel. These
have become almost routine, although they should not be. They occur most often in cases
of appointed counsel because it costs the defendant nothing to pursue the issue, and
there is a perception--incorrect in most instances--that appointed counsel is second
hand counsel. Retained counsel are just as apt to make mistakes as appointed counsel,
and the latter will not treat the case as a bothersome afterthought. Any attorney who
does so is subject to severe sanction which he does not wish to
face.

So to answer your question, from the facts presented,
I frankly do not see reversible error. Post conviction relief is more often than not the
result of a defendant unhappy with the outcome rather than a genuine failure of counsel
to represent him adequately.