Typescript can't be compiled in vs code: error TS5007

I just installed vs code v1 (the latest version) and typescript v1.8.10 (latest version). I followed the exact instruction from vs code website but can't get vs code to build the simplest typescript file though I can manually build it by running tsc command in git bash. The output from the vs code is:

error TS5007: Cannot resolve referenced file: '.'.
error TS5023: Unknown option 'p'
Use the '--help' flag to see options.

This is the my helloworld.ts file which really can't be simpler:

class Greet {
    private _message : string;
    constructor(message : string) {
        this._message = message;
    }
    Say = () => console.log(this._message);
}

var g = new Greet('hello typescript!');
g.Say();

This is my tasks.json file:

{
    // See http://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "0.1.0",
    "command": "tsc",
    "isShellCommand": true,
    "args": ["-p", "."],
    "showOutput": "silent",
    "problemMatcher": "$tsc"
}

and tsconfig.json:

{
    "compilerOptions": {
        "target": "es6",
        "module": "commonjs",
        "sourceMap": true
    }
}