siunitx in scrreprt - problems with beamer class

Question

I want to use the usepackage siunitx for my thesis (scrreprt). MikTeX asks for installing the documentclass beamer each time when I compile my document (and then freezes while installing). When I cancel the installation of the beamer package, the document is compiled correctly and displays the correct number with SI unit.

Here is a small example:

\documentclass[twoside]{scrreprt}
\usepackage{siunitx}
\begin{document}
\SI{5}{\micro\metre}
\end{document}

How can I avoid the installation message? It does not affect anything, it is just annoying.

Thank you!

*File List*  
scrreprt.cls    2012/07/29 v3.11b KOMA-Script document class (report)  
scrkbase.sty    2012/07/29 v3.11b KOMA-Script package (KOMA-Script-dependent basics and keyval usage)  
 scrbase.sty    2012/07/29 v3.11b KOMA-Script package (KOMA-Script-independent 
basics and keyval usage)  
  keyval.sty    1999/03/16 v1.13 key=value parser (DPC)  
scrlfile.sty    2012/06/15 v3.12 KOMA-Script package (loading files)  
tocbasic.sty    2012/04/04 v3.10b KOMA-Script package (handling toc-files)  
scrsize11pt.clo    2012/07/29 v3.11b KOMA-Script font size class option (11pt)  
typearea.sty    2012/07/29 v3.11b KOMA-Script package (type area)  
 siunitx.sty    2013/03/11 v2.5q A comprehensive (SI) units package  
   expl3.sty    2013/03/14 v4469 L3 Experimental code bundle wrapper  
 l3names.sty    2012/12/07 v4346 L3 Namespace for primitives  
l3bootstrap.sty    2013/01/08 v4420 L3 Experimental bootstrap code  
  luatex.sty    2010/03/09 v0.4 LuaTeX basic definition package (HO)  
infwarerr.sty    2010/04/08 v1.3 Providing info/warning/error messages (HO)  
ifluatex.sty    2010/03/01 v1.3 Provides the ifluatex switch (HO)  
    etex.sty    1998/03/26 v2.0 eTeX basic definition package (PEB)  
luatex-loader.sty    2010/03/09 v0.4 Lua module loader (HO)  
pdftexcmds.sty    2011/11/29 v0.20 Utility functions of pdfTeX for LuaTeX (HO)  
 ltxcmds.sty    2011/11/09 v1.22 LaTeX kernel commands for general use (HO)  
   ifpdf.sty    2011/01/30 v2.3 Provides the ifpdf switch (HO)  
l3basics.sty    2013/01/10 v4428 L3 Basic definitions  
 l3expan.sty    2013/02/03 v4458 L3 Argument expansion  
    l3tl.sty    2013/01/08 v4415 L3 Token lists  
   l3seq.sty    2013/01/12 v4434 L3 Sequences and stacks  
   l3int.sty    2013/01/13 v4444 L3 Integers  
 l3quark.sty    2012/11/04 v4268 L3 Quarks  
   l3prg.sty    2013/02/13 v4459 L3 Control structures  
 l3clist.sty    2013/01/08 v4414 L3 Comma separated lists  
 l3token.sty    2013/01/10 v4428 L3 Experimental token manipulation  
  l3prop.sty    2013/01/09 v4423 L3 Property lists  
   l3msg.sty    2013/01/08 v4412 L3 Messages  
  l3file.sty    2013/01/14 v4446 L3 File and I/O operations  
  l3skip.sty    2013/01/13 v4444 L3 Dimensions and skips  
  l3keys.sty    2013/02/24 v4461 L3 Experimental key-value interfaces  
    l3fp.sty    2013/01/19 v4449 L3 Floating points  
   l3box.sty    2013/01/08 v4411 L3 Experimental boxes  
l3coffins.sty    2012/09/09 v4212 L3 Coffin code layer  
 l3color.sty    2012/08/29 v4156 L3 Experimental color support  
l3luatex.sty    2012/08/03 v4049 L3 Experimental LuaTeX-specific functions  
l3candidates.sty    2013/03/14 v4468 L3 Experimental additions to l3kernel  
  xparse.sty    2013/03/12 v4467 L3 Experimental document command parser  
 amstext.sty    2000/06/29 v2.01  
  amsgen.sty    1999/11/30 v2.0  
   array.sty    2008/09/09 v2.4c Tabular extension package (FMi)  
l3keys2e.sty    2013/03/12 v4467 LaTeX2e option processing using LaTeX3 keys  
graphics.sty    2009/02/05 v1.0o Standard LaTeX Graphics (DPC,SPQR)  
    trig.sty    1999/03/16 v1.09 sin cos tan (DPC)  
graphics.cfg    2007/01/18 v1.5 graphics configuration of teTeX/TeXLive  
  pdftex.def    2011/05/27 v0.06d Graphics/color for pdfTeX  
supp-pdf.mkii  
siunitx-abbreviations.cfg    2013/03/11 v2.5q siunitx: Abbreviated units  
  ts1cmr.fd    1999/05/25 v2.5h Standard LaTeX font definitions  
 ***********

Answer 1

It seems that you have a problem with your installation of MiKTeX, if it is the current one. I guess you have installed basic MikTeX? See the first line of your log file. Do you see This is pdfTeX, Version 3.1415926-2.5-1.40.14 (MiKTeX 2.9)?

If no, you should update.

If yes, your installations is faulty.

Try to reboot your computer. Do you still have the error? If Yes follow this:

1. Delete the old installation completly! including TeXnicCenter.
2. Download the installer for complete MiKTeX from http://www.miktex.org
3. Install complete MiKTeX
4. Download TeXnicCenter from http://www.texniccenter.org
5. Install TeXnicCenter. It should recognize that you have an installed MiKTeX.
6. Now compile your MWE 3 times. It should run. If not, you have a problem with your computer.

Edit: I compared your file list with mine. You are using old packages for siunits and expl3.sty. My File List says:

 siunitx.sty    2013/07/31 v2.5s A comprehensive (SI) units package
   expl3.sty    2013/07/28 v4582 L3 Experimental code bundle wrapper 

and you have version 2.5q (older) and v4469 (older). Please use the MiKTeX package manager to update your packages.