I was running into the problem where Silverlight was not working in IE on my Tablet PC. It would work just fine in Firefox, but not IE. Each time I'd try to view a page with Silverlight in it, I'd get the graphic indicating that Silverlight was not installed. I'd click on the link to install Silverlight and it looked like all would go well, but when I'd try refreshing the page with Silverlight, I'd get the same graphic saying that Silverlight needed to be installed.
The problem turns out to be due to the fact that I previously had the February Silverlight CTP installed on my system and one of its DLLs needed to be re-registered.
Here are the steps to follow on your machine if you can't get Silverlight working on your system:
1. First, make sure that only one instance of Silverlight is installed on your system. To do this scan through all your installed apps in the Control Panel. Uninstall any older versions of Silverlight, if needed.
2. In Vista, you'll want to Run launch the DOS prompt using Adminstrator priviledges. To do this, click on the Start menu, select All Programs, then Accesories, then right click on "Command Prompt" and select "Run as Administrator" in the context menu that appears.
3. In the console window that pops up, change the current directory to where you have Silverlight installed. Typically this is:
cd c:\Program Files\Microsoft Silverlight
4. Register the Silverlight DLL npctrl.dll in the Silverlight folder by typing at the console prompt: regsvr32 npctrl.dll.
If you get an error dialog with the message: "The module "npctrl.dll" was loaded but the call to DllRegisterServer failed with the error code 0x80070005," then this means that you did not have permission to access the DLL as needed. Most likely you launched the command prompt using non-Administrator priviledges. To fix this problem, go to Step 2 in the steps above.
Once you do this, you should be able to run Silverlight in the IE.
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