Error: EXDEV: cross-device link not permitted, rename nodejs

I upload file with formidable , but I get this error

Error: EXDEV: cross-device link not permitted, rename

Here is my code :

router.post('/file',function(req,res) {
    var form = new formidable.IncomingForm();

function checkFile(filename) {
     if(filename.match(/\.(jpg|jpeg|png)$/i)){
       return form.uploadDir = path.join(__dirname, '../public/uploads/img');
    }else{
       return form.uploadDir = path.join(__dirname, '../public/uploads');
    }
}

  form.multiples = true;
    form.maxFieldsSize = 2 * 300 * 300;
   // every time a file has been uploaded successfully,
  // rename it to it's orignal name
  form.on('file', function(field, file) {
    var fileName = file.name;
    var d = new Date();
    var t = d.getTime();
    var newName = md5(file.name) + t;
    fs.rename(file.path,path.join(checkFile(fileName),newName),function(err) {
        if(err)
            console.log(err);
        console.log('Success')
    });

});
   // log any errors that occur
    form.on('error', function(err) {
        console.log('An error has occured: \n' + err);
    });


    // parse the incoming request containing the form data
    form.parse(req, function(err, fields, files) {
    });
})

When I remove function checkFile and change to form.uploadDir = path.join(__dirname, '../public/uploads'); , it work perfect . Where is my wrong ? Please help me

via Thanh Tùng