I use Texstudio and Miktex on Win 7 as a portable version.
Today i updated my miktex-packages and everything worked fine except the "\usepackage{tikz}" command.
I made a fresh reinstall with the newest versions of miktex and texstudio, opened my latex-document and compiled it. Miktex installed all missing packages on-the-fly except pgf/tikz, wich gave an error instead. I installed it manually in the package manager but texstudio still says "File "tikz.sty" not found".
Unfortunately I have to use the portable version, because I don't have any admin rights. The last time I worked on that document, everything worked fine.
Any ideas?