Invalid Filename- Download file

Question

it('Empty download folder  - Sponsor', function () {
    applicationHelper.emptyFolder(dirPath);
    rimraf(dirPath + '*', function () {
        console.log('done');
    });
});
it('Download draft ct - Sponsor', function () {
    clinicalTrialsPage.downloadCt();
    pagesNavigation.navigateToByName('Applications');
    clinicalTrialsPage.selectDownloadOptionsforPartI();
    expect(topBanner.getMessageInToast()).toContain('Successfully Downloaded');
    browser.sleep(10000);
});
it('Check contents of zip', function () {
  let downloadedZip = glob.sync(dirPath + ctNumber + '*.zip');
    var zipFile = fs.readdirSync(dirPath);
    console.log(zipFile);
    zip = new admZip(dirPath + zipFile[0]);
    zip.getEntries().forEach(function (entry) {
        console.log(entry.entryName);
        zipEntry.push(entry.entryName);
    });
    zip.extractAllTo(dirPath + "zip/", false);
    expect(fs.existsSync(downloadedZip[0])).toBeTruthy();
});

I want to check that the downloaded file exists (which it does) but the script keeps failing, with the error invalid filename. The console.log(zipFile) gives a proper result. I use ChromeDriver for Selenium Protractor and the config.js is properly set up (capabilities,prefs etc) Any ideas?