Visual Studio nmake Ruby

i got problems with building Ruby by Visual Studio nmake.
I fallow the instructions in \ruby-2.1.2\win32\README.win32. But allways
when i try to run the configure.bat i get this error-message:
NMAKE : fatal error U1077: “cl”: Rückgabe-Code “0x2”
What i do wrong?

My Solution:
First execute
C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat
from commando line and then fallow the instructions in README.win32.