Ad Logicam is one of the Fallacious Arguments where it is asserted that because an argument contains a fallacy, the conclusion must be false.
See also www.fallacyfiles.org 
The rest of this page is no longer talking about Ad Logicam ...
Some teminology. Given a statement P-->Q:
P is the antecedent
Q is the consequent
The inverse is ~P-->~Q
The converse is Q-->P
The contrapositive is ~Q-->~P
P->Q <=> ~Q->~P
P->Q <=/=> Q-> P
None of this has anything to do with Ad Logicam.
Also known as Disproof By Fallacy
See original on c2.com