Could not load file or assembly 'Microsoft.Windows.Design.Extensibility ...'

• Sep 27, 2023

Error Description

When you use DevExpress ASP.NET products together with the AjaxControlToolkit, the following errors can occur:

• Could not load file or assembly ‘Microsoft.Windows.Design.Extensibility …’
• Could not load file or assembly ‘X’

This problem usually occurs when DevExpress.*.Design.dll assembly files exist in the application Bin folder. These files are intended for development purposes only. Note that DevExpress.*.Design.dll assembly files cannot be distributed according to our EULA terms.

Solution

1. Remove all DevExpress.*.Design.dll files from the application Bin folder and exclude them from deployment.
2. Clear the following directory: **C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files**.
3. Rebuild the application.
4. Redeploy the application without DevExpress.*.Design.dll assembly files.