Does the S: drive exists or is mapped? Do you have write access on that drive?
Comment the "SandboxPath" parameter by adding a semicolon (;) before in the package.ini and rebuild by executing the build.bat. The sandbox will be created at the default location which is %APPDATA%\Thinstall.
SandboxPath Parameter
The SandboxPath parameter determines the path to the sandbox.
The path to the sandbox can be relative or absolute, can include folder macros or environment variables, and
can exist on a network drive.
You might work with the SandboxPath parameter to address local, USB drive, or network needs, to address
space limitations in the initial sandbox location, or to move the sandbox to the desktop for troubleshooting
purposes. The sandbox path does not include the sandbox name because the SandboxName parameter
determines that name.
