ghostScript with Node generates fatal error

I'm using ghostscript with Node (running on MacOX and Ubuntu). my ghostscript command is this:

/usr/local/bin/gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=output.pdf -dBATCH input1.pdf input2.pdf 

When I run this command manually, it works. When it's kicked off by NodeJS, I get this error:

[2014-09-08 10:33:20.587] [INFO] console - { [Error: Command failed: GPL Ghostscript 9.10: Unrecoverable error, exit code 1
] killed: false, code: 1, signal: null }
Error: Command failed: GPL Ghostscript 9.10: Unrecoverable error, exit code 1

at ChildProcess.exithandler (child_process.js:647:15)
at ChildProcess.EventEmitter.emit (events.js:98:17)
at maybeClose (child_process.js:753:16)
at Socket.<anonymous> (child_process.js:966:11)
at Socket.EventEmitter.emit (events.js:95:17)
at Pipe.close (net.js:465:12)

Node code looks like this:

var execCommand = config.ghostScript + " -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=" + finalFileName + " -dBATCH " + inputFiles;
exec(execCommand, function (error, stdout, stderr) {
    if ( error !== null ) {
        var err = new Error("pdf could not be generated");
        err.status = constants.HTTPCODE_INTERNAL_SERVER_ERROR;
        throw err;
    } else {
        console.log("success");
    }

Any ideas?