BibTeX, biblatex and biber ⇒ natbib issue

[lucky]

Hi
I have 2 PC, one with Miktex 2.6 the other with miktex 2.7
For the same project (TeXnicCenter) I have absolutely no problem with the 2.6 release but with the 2.7 natbib seems not to be recognized. Each \citep generates an error while there is no error with \usepacakge{natbib}
Could somebody help me to solve my problem.

[josephwright]

Include \listfiles in your input and post the log files here.