I've been scratching my head on this for a while. The error occurred with Firefox 28 and Silverlight 5. Reinstalls, clearing session, deleting C:\ProgramData\Microsoft\PlayReady\mspr.hds all did nothing.
The working solution was straightforward in the end:
- Run C:\Program Files\Microsoft Silverlight\5.1.30214.0\Silverlight.Configuration.exe, then click on 'Application Storage' and 'Delete All'. Ensure 'Enable Application Storage' is left ticked.
- Close all browsers then navigate to C:\ProgramData\Microsoft\PlayReady and delete mspr.hds.
- Right-click the Firefox taskbar icon, then right-click on 'Mozilla Firefox' and choose 'Run As Administrator'.
- Once Firefox is launched, select 'Help' and 'Restart with Add-ons Disabled'.
- When Firefox launches, select 'Safe Mode' and wait for Firefox to launch.
- Browse to Netflix and watch a film.
- Close Firefox and restart it.
I hope this helps anyone else getting the same issue.