Performative contradiction.

In an article I read recently the author suggested that,
     'Foucault is involved in performative contradiction in so far as 
      he cannot argue for the value of his epistemic position without 
      having its conclusions undermine the assumptions they require 
      for their articulation.'
This is not the first time I have met this argument.  One neo-marxis 
critique I read on Foucault accused him (and Derrida) of a similar 
faux pas, 
     '....like all relativist philosophers, Foucault is open to 
      questions about his own grounding.  How can Foucault know what 
      he claims without some general concepts, without a theory?'
What do you think, did Foucault shoot himself in the foot?

Also, I have been thinking a little bit recently about Gramscis notion 
of Hegemony and trying to link this with some of Foucaults work (if
anyone is interested in this I came across an interesting article by 
Barry Smart in 'Foucault, a Critical Reader'