Getting things wrong, some examples.

 Perloff and Bernstein calling poems "iambic pentameter" when they are not.  http://itre.cis.upenn.edu/~myl/languagelog/archives/001165.html

At the time, I commented:  

The Bernstein example is actually worse, because he is making an argument that depends on the lines quoted being in iambic pentameter, the "meter of the empire." Perloff, who wrote her dissertation on rhyme in Yeats, was probably suffering from a moment of inattention, a momentary lapse such as could occur to any of us. She has many competent scansions in her critical works and is one of the contemporary  critics who pays most attention to form.

Whole disciplines based on sandy gr0und. 

Lazy thinking.

I guess we would have to distinguish between random error at the edge (unavoidable) and systemic error.