An Error Has Occurred:
Silverlight Tools cannot be installed because one or more of the following conditions is true:
1. Visual Studio 2008 RTM is not installed.
2. The Web Authoring feature of Visual Studio is not installed.
3. A previous version of the Silverlight Runtime is installed.
4. A previous version of the Silverlight SDK is installed.
5. The Visual Studio Update KB949325 is installed.
6. A previous version of Silverlight Tools is installed.
To continue, please install or uninstall the appropriate products and run this installer again.
Short Answer: You are sure that all of conditions above are false but you are getting this error. Then, The shortest answer is "uninstall Silverlight 2 beta1 SDK" from your machine.
That's all. You should be able to install after uninstalling. but If you want to read more details, please keep on reading further.
Step #1. Install Visual Studio 2008 release version or RTM version
You have to install the release or RTM version of Visual Studio 2008 in your machine. Your Visual Studio should be Professional Edition or Standard Edition or Team System. You can't use VS 2008 beta or Express version.
Step #2. Install the Web Authoring Component of Visual Studio
You need to check whether you have Microsoft Visual Studio Web Authoring Component installed in your machine or not. If you have installed Visual Studio 2008, you already have that web authoring component installed. but just in case you accidentally remove that component, you can run WebToolsCore.exe to install that component manually. The setup fiel is located under WCU\WebToolsCore of VS DVD. If you are not sure about what VS Web Authoring Component is, you can read this post.
Step #3. Remove the Visual Studio Update KB949325 if it's installed
You have to remove that Visual Studio Update (KB949325) from your machine.
If you are a Windows Vista user, please go to "Control Panel" and open "Programs and Features". Then, Click "View installed updates" and find "KB949325".
If you are XP users, go to "Add and Remove Programs" and select "Show Update". And find "KB949325" in the list.
Step #4. Uninstall all of the previous versions of the Silverlight Runtime/SDK/Tool
You have to uninstall all of the previous versions of Silverlight runtime/SDK/Tool from your system.
Uninstalling is very simply. but sometimes, you might face some weird problems. One of my friends faced one weird problem when he tried to uninstall the previous version of Silverlight. He installed "Silverlight 1.0 SDK VS 2005 template" in his machine long time back. The time when he installed that SDK, he had VS 2005.
but after sometime, he removed VS 2005 from his machine. Now, he wanted to remove SL 1.0 SDK but he couldn't. The message below kept on showing when he tried to uninstall.
So, I suggested him to use Windows Installer CleanUp Utility to remove that SDK and he did it.
Note: I would like to suggest you to use CCleaner to scan your registry and fix all issues after removing SL 1.0 SDK from your machine.
Step #5. Uninstall Silverlight 2 (beta1) runtime, SDK, Tool for Visual Studio 2008
Please uninstall Silverlight 2 (beta1) runtime, SDK, Tool for Visual Studio 2008 in case you have installed before facing this problem.
Step #6. Install Silverlight 2 (beta1) runtime
Now, you can install Silverlight 2 (beta1) runtime. (It's just for the sequence of installing. That's why I asked you to uninstall SL2-related things first.)
Step #7. Install VS 2008 Web Development Hot-Fix
You can download this hot-fix from this link. then, install it in your machine after installing Silverlight 2 runtime.
Now, you can run silverlight_chainer.exe again.I hope you should be able to run the setup successfully. Feel free to let me know if you have any problem in installing SL 2 Tool.
Issues after installing Silverlight 2 Tool for VS 2008
#1: 'Microsoft.VisualStudio.Web.Silverlight.IVsSilverlightService' error
If you are getting one of the following error, you have by-passed the validation of Silverlight 2 Tool installer by extracting (winrar-ing) the silverlight_chainer.exe or following this post. You have to follow 7 steps that I mentioned above to install Silverlight 2 Tool firstly. If you are able to install that tool, the following error will be disappeared.
#2. The project type is not supported by this installation
Run devenv.exe /resetskippkgs in case you got this error. (Thanks to BradleyB for this post.)