Create directory fails on Android

The code works on PC.  The directory is successfully created under My Documents.  But somehow it is not working on Android.

var workDirectory:File = File.documentsDirectory.resolvePath("testDir/tempDir");

if (!workDirectory.exists) {

     workDirectory.createDirectory();

}

I have already added this in the manifest:

<uses-permission android:name="android-permission.WRITE_EXTERNAL_STORAGE" />

The workDirectory.url is file:///mnt/sdcard/testDir/tempDir

The SD card is good.  I can create the directory manually on the Android tablet.

I am running AIR2.5 and Android 2.2.

Any help is appreciated.

Thanks in advance!