epup to sd card with smartphone not working

Hi,

I am trying to copy an epub from my Android phone to my reader (Sony PRS-T2) using a SD-Card.

When I put the SD-Card in my reader the epub shows up, but when I try to open it it says the file is DRM-protected.

- My reader is activated using the same Adobe-ID as I used on my phone.

- I downloaded an ACSM-file from my public library and used the Adobe Digital Editions App to get the epub.

- I can read the ebook on my phone.

- I can transfer epub-files from my computer (Win) to the reader (drag&drop, even without using ADE) and open and read them on the reader.

- I will be traveling with only my phone and my reader, so using my computer won't be an option.

What is the problem here? Is there a special way to sync the sd-Card with the reader or do I need to put the file into a particular folder on the sd-card or do I need to copy additional files?

Help is much appreciated!