
I just recently upgraded to Visual Studio 2008 Professional and installed the RadControls for ASP.NET AJAX product suite (RadControls_for_ASP.NET_AJAX_2008_3_1314_dev.exe). All is well except that when I create a new VS2008 ASP.NET website project, the toolbox has a tab labeled “RadControls for ASPNET AJAX Q3 2008” and lists all the individual controls. The problem is that all the controls on this tab are grayed-out and cannot be dragged to a aspx page to begin using the controls.
I have attempted several things to see if I could fix this issue without any success. Here is what I have tried.
1. I ran the “ToolBoxInstaller.exe” program that is included in the RadControls install…no change.
2. I added a reference to the “Telerik.Web.UI.dll” in the project references…no change.
3. I manually added the controls to the ToolBox by browsing to the “Telerik.Web.UI.dll” in the Bin35 folder…no change.
I am at a loss as to what is causing this issue. Any guidance would be appreciated.
5 Answers, 1 is accepted

For me sounds like a problem with the registry or something about your PC
My recommendation is,
Uninstall Telerik suite
Run CCleaner (You can download if you don't have, it's Free, ask Google where ;-) )
Use Cleaner Tab (My recommendation is mark every option) and erase all the temps
Use de Tab "Registry" and Scan until you don't have any Issue
After all this I recommend you restart your pc
And later reinstall Telerik suite
I hope this works for you
Greetings!!

I also ended up uninstalling the RadControls for ASP.NET Q2 2008 that I had installed for another application that uses that version. I simply kept the DLLs so that app would still run properly. So here is my final configuration and it is working properly:
Vista Business SP1
Visual Studio 2005 Professional SP1
Visual Studio 2008 Professional
RadControls for ASP.NET AJAX Q3 2008
RadControls for ASP.NET Q2 2008 (DLLs only)
ASP.NET 2.0 AJAX Extensions 1.0
I'm still not quite sure what was causing the issue, but it seems to be working properly now, so hopefully it will remain that way. Thanks for the suggestions!

If anyone else has stumbled upon this problem and has any suggestions for fixing it, I absolutely welcome your comments as this problem is really quite frustrating.
I'm starting to wonder if it has anything to do with having two development setups on the same machine. Since I am still developing a ASP.NET 2.0 application with VS2005 and at the same time working on a newer ASP.NET 3.5 application with VS2008 I have both of these development setups on the same machine...just a thought.
Again any suggestions are appreciated!
I think that the information from the following public forum posts will help you address the abnormality in question:
http://www.telerik.com/community/forums/aspnet-ajax/general-discussions/unable-to-add-telerik-web-ui-dll-to-the-visual-studio-2008-toolbox.aspx
http://www.telerik.com/community/forums/aspnet/general-discussions/toolbox-controls-not-available-for-asp-net-forms-in-vs2008.aspx
Best regards,
Sebastian
the Telerik team
Check out Telerik Trainer, the state of the art learning tool for Telerik products.

The second link you provided, is a more developed discussion of the same exact problem I am experiencing. I'm not sure why I didn't run across it as I was searching the forums before starting this thread, but I will continue my discussion on that thread as it has a lot more activity.
http://www.telerik.com/community/forums/aspnet/general-discussions/toolbox-controls-not-available-for-asp-net-forms-in-vs2008.aspx
Regards,
Kenyon