If you are using Internet Explorer, be sure you have added "*.netflix.com" without the quotes to your trusted sites. If you need instructions on how to add a new trusted site, see surfthenetsafely.com: Trusted Sites
. Also, if you have "Require https" checked under your trusted sites settings, you must uncheck this option because netflix does not use https.
Do you have "playback of protected content" enabled in your silverlight settings? If you don't know,
1. open the Silverlight Configuration here -> On 64-bit operating systems: C:\Program Files (x86)\Microsoft Silverlight\versionNumber\Silverlight.Configuration.exe.
2. Click the "Playback" tab.
3. Choose "Enable playback of protected content", if not already toggled.
"The Playback tab allows users to enable or disable playback of content protected by digital rights management (DRM)." From Microsoft Website: Microsoft Silverlight Configuration
If playback of protected content is already enabled, or if enabling it doesn't work, Clear your Silverlight Data Storage. This will remove the device ID assigned by Netflix so a new one can be generated the next time. This also helps if Silverlight is crashing because your data was full/near full in the first place.
1. Re-open the Silverlight Configuration Dialog box.
2. Click on "Application Storage" tab. Be sure that "Enable Application Storage" box is checked.
3. Click "delete all" then Click "OK."
-If for some reason you cannot access the Silverlight Configuration, you can clear your Silverlight Data Storage manually. To do this:
Delete the Silverlight folder from C:\Users\UserName\AppData\LocalLow\Microsoft\
- If you do not see the AppData folder, You will have to show hidden files and folders. For help on this see Microsoft: Show hidden files and folders
NOTE: After deleting the Silverlight folder, follow the same process and click "Do not show Hidden Files, Folders and drives" to re-hide those folders.
See if those options help.