Design-Time Errors Occur on a Page Using Telerik Controls

Environment

Product

Progress® Telerik® UI for ASP.NET AJAX

Description

When working with Telerik UI for ASP.NET AJAX or dragging a Telerik control from the ToolБox to the design surface, design-time errors occur on a page that uses Telerik controls.

Causes

Depending on the use case, the possible causes for such errors may be the following:

• If the Telerik.Web.UI.dll assembly is updated while a page using Telerik controls is in Design-time, Visual Studio creates two different versions of the assembly. Hence, two different versions of the same Telerik controls are available.

• If you try to drag a Telerik control from the Toolbox to the design surface and get an error, the possible reasons are various. Refer to the resource links below.

• After upgrading Telerik UI for ASP.NET AJAX to Q1 2009, Visual Studio 2008 has a problem with loading GAC-ed design-time assemblies of control libraries deployed in the Bin folder of a website.

Error Messages

• (Two assembly versions) Error Creating Control - Telerik control 'Property' cannot be initialized. Details: Unable to cast object of type 'Type' to type 'Type'

• (Dragging a Telerik control from the ToolBox) Error creating control. Unable to cast object of type 'Telerik.Web.UI.Radxxx' to type 'Telerik.Web.UI.ControlItemContainer

• (Problem loading GAC-ed assemblies) Error creating control - ControlName or Failed to create designer "Telerik.Web.UI.ControlName..."

Solutions

Depending on the possible cause for this issue, use the following approaches to handle it:

• (Two assembly versions) Restart Visual Studio.

• (Dragging a Telerik control from the ToolBox) Refer to the following resources:

  • Error rendering control (Unable to cast object of TypeA to TypeA)
  • Menu problem: Error creating control at design time
  • Clearing Cache
  • Visual Studio: Error Creating Control

• (Problem loading GAC-ed assemblies) To solve this issue, use any of the following approaches:

  • To Bin-deploy the design-time assembly, add a reference to Telerik.Web.Design.dll to your website or application, remove Telerik.Web.Design.dll from the GAC, and restart Visual Studio.

  • To GAC-deploy the control library assembly, add Telerik.Web.UI.dll in the GAC, remove Telerik.Web.UI.dll from your Bin folder, and restart Visual Studio.

  • Copy Telerik.Web.UI.dll to C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE\PublicAssemblies and restart Visual Studio.