Looks like I've found the culprit of this problem.
Sometimes the automatic date and time configuration makes the time and date messed up, therefore if the time/date and timezone are not right, the device can't connect to DRM servers, or if my analysis is right, that the DRM info is time/date stamped, so if the file played outside its specified time/date, it needs to re-sync to DRM servers to re-verify its permission.
The solution is fairly simple, you need to turn off your auto update time/date settings, and manually set the timezone, date and time. After its fixed, the downloaded file will play even you have no network connections, looks like the DRM info is stored in date/time basis.
I'm using Lumia 920, and this phone sometimes cannot wake up from sleep, then I have to soft-resets it by holding down vol-down+power button. after it boots up again, the time and date is always messed up. This is how I found the DRM problem and the solution.
PS :
- When you soft-resetting your phone, the time will always be messed up. It's best to set the date and time manually.
- Its best after fixing your date/time, you go to account settings and re-sync your Microsoft account.