Hi Pepe Le Pew,
yes, I had to install ROOT again, but now without the --prefix-blabla. Now everything works and I have no errors. But one little problem is still there! 
If I run a python-script with a ROOT-canvas, the canvas is only for a second visible. I am not sure, but I remember that I fix it when I type “ipython name.py”, but it doesn’t work.
And when i start ROOT, I get this:
Couldn't find font "-adobe-helvetica-medium-r-*-*-10-*-*-*-*-*-iso8859-1",
trying "fixed". Please fix your system so helvetica can be found,
this font typically is in the rpm (or pkg equivalent) package
XFree86-[75,100]dpi-fonts or fonts-xorg-[75,100]dpi.I have used this manual here. [url]Adobe helvetica on ubuntu 11.04 Please don’t say that I have to install ROOT again. 