I have a very simple ASPX page and followed the installation procedures for Telerik UI for ASP.NET AJAX, all seems good and no errors when entering the source ... but as soon as I hit "Design" tab in VS 2015 IDE to view I get the following error for any Telerik control reference:

 

I was able to solve this problem by following these procedures:

https://docs.telerik.com/devtools/aspnet-ajax/general-information/troubleshooting/design-time-troubleshooting

but the online documentation is NOT correct.  I'm running R3 2018 (2018.3.910.45) and this was the first time I've ever installed UI for ASP.NET AJAX (not an upgrade) ... the documentation suggest this problem was actually fixed in 2018.1.215.2 but obviously it was not fixed as I'm running with a more recent version.

I did copy the Telerik.Web.Design.DLL to my project's BIN folder, but that also required that I exit VS 2015 and restart VS 2015 with my project ... then I no longer got this error.

Is there going to be a corrected fix for this?  It's a rather obvious bug and will hit developers as soon as they try to use any telerik controls and switch to design view.

Cheers, Rob.

Hi Rob,

Can you please elaborate more on your scenario?

We just need to realize what the setup scenario is to see why the Telerik.Web.Design.DLL is not available in the bin folder.

• How did you setup the project? 
• Was it an existing project or you have created a new Telerik Web Application/Web Site from scratch? 
• Have you personally copied the Telerik.Web.UI.dll to the bin folder or it was already there?  
• Do you use the Visual Studio toolbox to insert the telerik:RadLightBox? 
• Which article did you follow to register the Telerik components? 

Thank you in advance!


Best regards,

Rumen
Progress Telerik

Hi Rumen,

Setup was done via the latest version of your Telerik Control Panel.

I was adding to an existing web application (combo web app that has standard ASP and Silverlight 5 and some web services).

I had to copy Telerik.Web.UI.DLL to bin folder and set a reference per documentation ... however the documentation is not providing the best solution, all I really needed to do was add the reference to my project and point to the install path for R3 2018 (C:\Program Files (x86)\Progress\Telerik UI for ASP.NET AJAX R3 2018\Bin45\Telerik.Web.UI.dll).

Yes I used the Toolbox to find and drag drop the RadLightBox.

I believe I used part of this article (but installation was done via Control Panel not via "Extensions and Updates": https://docs.telerik.com/devtools/aspnet-ajax/getting-started/first-steps

Cheers, Rob.

 

Thank you for the provided information, Rob!

I followed the provided steps and found that due to historical reasons the drag and drop from VS Toolbox does not register the Telerik.Web.Design.dll in the Bin folder. I filed an internal feature request for our VSX team and we will improve this.

As a small token of gratitude for your help on improving the productivity and getting started capabilities, I updated your Telerik points.

Best regards,
Rumen
Progress Telerik

Hey all,

We researched the issue and it appeared that due to limitations, we cannot register the Telerik.Web.Design.dll in the bin folder after dragging component from the Toolbox, because the toolbox can reference assemblies which contain controls only. The design dlls do not contain controls.

To notify the developers, I've updated the troubleshooting article with this extra information:

Note that the Telerik.Web.Design.dll cannot be added to the Bin folder when dragging and dropping a Telerik ASP.NET control from the Toolbox of Visual Studio. In this case, only the Telerik.Web.UI.dll is copied to the Bin folder and you will need to manually copy the Telerik.Web.Design.dll to the Bin folder and reference it.

Best regards,
Rumen
Progress Telerik