[Tex/LaTex] pgf install error – MiKTeX


i have this code taken from another question trying to produce a tree:

\tikzset{edge from parent/.style=
{draw, edge from parent path={(\tikzparentnode.south)
-- +(0,-8pt)
-| (\tikzchildnode)}}}
    [.Class  \edge[color=white]; 
    [.Order  \edge[color=white];
    [.Family \edge[color=white]; 
    [.Genus ]]]]};
        [.Alteromonadaceae  {Glaciecola}  Alteromonas Agarivorans ] ]
    [.Vibrionales [.Vibrionacae Vibrio ]]]};\\


but when compiling using TeXworks in MiKTeX 2.9 i always get the same error:

This is pdfTeX, Version 3.1415926-1.40.11 (MiKTeX 2.9)
entering extended mode
LaTeX2e <2009/09/24>
Babel <v3.8l> and hyphenation patterns for english, afrikaans, ancientgreek, ar
abic, armenian, assamese, basque, bengali, bokmal, bulgarian, catalan, coptic, 
croatian, czech, danish, dutch, esperanto, estonian, farsi, finnish, french, ga
lician, german, german-x-2009-06-19, greek, gujarati, hindi, hungarian, iceland
ic, indonesian, interlingua, irish, italian, kannada, kurmanji, lao, latin, lat
vian, lithuanian, malayalam, marathi, mongolian, mongolianlmc, monogreek, ngerm
an, ngerman-x-2009-06-19, nynorsk, oriya, panjabi, pinyin, polish, portuguese, 
romanian, russian, sanskrit, serbian, slovak, slovenian, spanish, swedish, swis
sgerman, tamil, telugu, turkish, turkmen, ukenglish, ukrainian, uppersorbian, u
senglishmax, welsh, loaded.
("C:\Program Files\MiKTeX 2.9\tex\latex\base\article.cls"
Document Class: article 2007/10/19 v1.4h Standard LaTeX document class
("C:\Program Files\MiKTeX 2.9\tex\latex\base\size10.clo"))
("C:\Program Files\MiKTeX 2.9\tex\latex\tikz-qtree\tikz-qtree.sty"
pdflatex.EXE: Cannot start MiKTeX package manager.
pdflatex.EXE: Data: The class is not configured to support Elevated activation.


! LaTeX Error: File `tikz.sty' not found.

Type X to quit or <RETURN> to proceed,
or enter new name. (Default extension: sty)

Enter file name: 

can you help me solve this issue, i really need to draw some trees in my thesis…
thank you.

as requested by Alan Munn, i tried to install pgf from the package manager, and received this error at the end of the download process:

MiKTeX Problem Report Message: The operation could not be completed because the following file failed verification: C:\Users\nagi\AppData\Local\Temp\mik2E71.tmp

i tried installing pgf again after some time, but with the same result (error).

Best Answer

Thank you all! With your feedback I was able get this example to run. I googled and installed manually the packages pgf and ms using the package manager. Hope MiKTeX will fix their repositories soon...