Option clash when using graphicx and tikz packages

The tikz package already loaded the graphicx package, so you can't load it again. Trying to load it with different options will cause the "Option clash" error. You can use \PassOptionsToPackage{<options>}{graphicx} before loading tikz to pass any additional options to the internally loaded graphicx. However, you do not need and should not use the pdftex option manually with modern LaTeX distributions. Packages which are driver dependent are very well capable to detect the right driver by themselves and providing a wrong one causes all kinds of trouble.

Put the tikz package before the graphicx package, that's what I did when I had the same problem by using the final option of the graphicx packages with the tikz package and it works.