Error: Unable to find vcvarsall.bat
Although I had Visual Studio 2010 installed, and made sure the batch file exists and the batch file creates the compilation environment correctly, I still got this error.
Googling the issue brought this question with this specific solution.
The short answer (credits to fmuecke) is to point the environment variable VS90COMNTOOLS to the value of VS100COMNTOOLS.
This solved the issue.