DO use IF ERRORLEVEL 1 ECHO error level is 1 or more to check for errors in your batch/command line scripts.

DO NOT use IF %ERRORLEVEL% NEQ 0 ECHO error level is not equal to 0.

Most of the time %ERRORLEVEL% will be what you expect but it isn’t guaranteed. %ERRORLEVEL% is simply an environment variable like any other. It just happens to fallback to returning the ERRORLEVEL value if an environment variable with that name isn’t defined.

This is how I lost about an hour of my morning. Fortunately Google guided me to this excellent post and saved my sanity.

Remember %ERRORLEVEL% is not the same as ERRORLEVEL.