Need help with drm-removal from Storytel

[Ahemait]

I started an account on storytel yesterday and wanted to remove the drm so I can listen on the files were ever I want. First opsticle is that you aren't allowed to download audiobook to an offline state on the computer. I downloaded the file via my tablet and transfered it into the PC.
Second problem is that no program I've tried (either on the tablet or pc) can recognize the file. It's listed as an Mp3, but not winamp, vlc, aimersoft och digital media converter can open it.
These are the messages I get:

* Format not supported
* Empty file
* This is not a Mp3 file

I've tried to just rename it to some other file-format, but if that'd worked it would almost have been to easy
Anyone know how to get around this, or how storytel have managed to create a Mp3-file that isn't a Mp3-file?

[Q91]

It can be a MP3, but the file is encrypted, so only software that knows the encryption can store the file in memory so it can playback it

[Ahemait]

Do it have to be the program used by storytel, or should any encryption program be able to crack it?