Continuing the discussion from Workaround for sen2cor bug at resolution 10 m, with a nod to this “unrecognized variable” topic:

If you get a KeyERROR 'SEN2COR_HOME' you might want to make sure that you installed Sen2Cor according to the SETUP.pdf, and that you have an environment variable called SEN2COR_HOME.

To check for that environment variable on a Windows system, you can either

a) follow the instructions on How To Manage Environment Variables in Windows (XP) and

  1. Right-click My Computer, and then click Properties.
  2. Click the Advanced tab.
  3. Click Environment variables.
  4. Look for a variable called SEN2COR_HOME in either User or System Variables.

or you can
b) list the environment variables in a command window and look there, like this:

  1. Click the Start button (or press the Windows key).
  2. In the search box at the bottom of the Start menu, type cmd and press Enter.
  3. In the Command Prompt window that should have popped up now, type set and press Enter.
  4. Look for a variable called SEN2COR_HOME in the list of environment variables.

If you don't find a `SEN2COR_HOME` environment variable then your Sen2Cor setup probably failed -- you might want to retry.