This question is really directly to Spotify support but I couldn't see a way of contacting them other than here.
I have an Asus Transformer Prime running Android 4.0.3 and the latest version of Spotify with a Spotify Premium account.
Offline mode doesn't play my downloaded tracks saying (incorrectly) that my license has expired so I do the following:
1. I uninstall Spotify from the tablet.
2. I reinstall using the latest software and put my account credentials in.
3. I download a few tracks for offline listening (my tablet doesn't have a 3g capability so this is the only way I can listen using the device if I am mobile).
4. The device tells me I only have 29 days left to listen to the tracks and need to go online.
5. I go online immediately for an hour or so.
6. I switch spotify to offline mode and it tells me I only have 29 days left to go online.
7. After 29 days, Spotify tells me offline listening is disabled as my license has run out.
8. It hasn't and that's why I'm paying for Premium.
9. I need to start from to step 1 above and download everything again.
Sounds like a critical software bug to me with pretty harsh commerical consequences, that by the looks of it through searching, quite a few people experience and haven't solved. Or am I particularly unlucky.
Spotify suport, what steps should I take so I can use my premium subscription offline on my Android tablet?