Folder can't be deleted?

I installed the Galaxy S3 Retail Mode found in Google Play but had problems setting it up so I uninstalled it.

Now, I have a folder in /sdcard/ named RetailMode that contains photos used by the RetailMode application. But no matter what I do, I can't delete it. Can't delete any of the photos either.

I tried changing owners and changing permissions but failed. I even tried via adb shell.

Any ideas of how I can delete it?

Thanks in advance!