Affirming the Consequent
http://www.datanation.com/fallacies/affirm.htm

Definition:
Any argument of the following form is invalid:
If A then B
B
Therefore, A

Examples:
(i) If I am in Calgary, then I am in Alberta.
    I am in Alberta, thus, I am in Calgary.
    (Of course, even though the premises
     are true, I might be in Edmonton, Alberta.)

(ii) If the mill were polluting the river then we would see an
    increase in fish deaths. And fish deaths have increased. Thus,
    the mill is polluting the river.

Proof:
Show that even though the premises are true, the conclusion
could be false. In general, show that B might be a
consequence of something other than A. For example, the fish
deaths might be caused by pesticide run-off, and not the mill.

References
Barker: 69
Cedarblom and Paulsen: 24
Copi and Cohen: 241