[RESOLVED]Error Creating Control

Hi, I´ve just installed a VWD 2008 Express and when I try to add any component from the Toolbox in the form, the message "Error Creating Control – <name of component>. Duplicate component name <name of component>. Component names must be unique and case-insensitive."
stay in the place of the component.

I´ve already uninstall and reinstall the VWD 2008 Express, but not solve the trouble. Please, someone can help me? Thanks.

Please check version of the System.Web.Extensions and System.Web.dll. It should be 2.0.50727.1427 or later: perhaps you have prerelease framework installed. Similar issue is documented here:

HI, I know this thread happened a while back, but if anyone see’s this…

… I have Visual Web Developer 2008 Express Edition & the SQL 2005 installed on my system. It was all working fine till a week or two ago. But now when I try to add a any standard control in design view I get the error:

"Duplicate component name ‘<component name>’. Component names must be unique and case-insensitive."


Even when I open old projects that were working fine earlier, controls are now replaced with a box with error:

"The type initializer for ‘Microsoft.Web.Design.ExtenderInformationServiceProvider’ threw an exception."

Have tried reinstalling Visual Developer.

Also the hot fix listed in the post above is for Visual Developer 2005, when I try to install it says program isn’t installed or different version.


Any help so as to how to fix this? Any patch for 2008?

Also if I want to remove Visual Developer completely from the system and start an install from scratch what all do I uninstall?

 Any help would be really appreciated.



This has nothing to do with VWD itself, the problem, as indicated above, is in .NET framework install (System.Web or System.Web.Extensions is incorrect). Try reinstalling .NET 3.5 and please verify assemly versions as indicated above.

Nice one, adding a reference to System.Web.Extensions solved this issue for me two years later!

Thanks Mikhail. 

Hello, I have the same problem. I have Visual Studio 2010

Microsoft Visual Studio 2010
Version 10.0.30319.1 RTMRel
Microsoft .NET Framework
Version 4.0.30319 RTMRel

Installed Version: Professional

I set my project target framework as .net 3.5, but I have the similar error:

Error Creating Control - PasswordRecovery1Duplicate component name 'PasswordRecovery1'. Component names must be unique and case-insensitive.
I tried to download the hotfix but it says different version and unavailable something. Thanks for help.

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