Extender Provider failed to return an Extender

Question

We upgraded from .NET 2.0 to .NET 3.5. A co-worker of mine is getting the following dialog when attempting to run the ASP .NET web project under the debugger in Visual Stud

Answer 1

In VSTO, you can't use the designer while debugging another VSTO app.

For example, if another VSTO debugging session is running and you try to invoke the Excel Designer on a different project, you'll get "The Extender Provider failed to return an Extender for this object". Stop debugging to free up the Designer.

Answer 2

In Visual Studio 2019 I had several webservices in a solution failing to load with this error. In my case the error was caused because I had changed the port numbers in IIS for those web services meaning the port numbers in .csproj and/or csproj.user did not match IIS. As soon as I updated the .csproj port numbers to match IIS, the error went away.

Answer 3

I had this problem because a project used IIS and HTTPS, there was no https binding on the IIS, adding a HTTPS binding on the default website fixed the problem.

Answer 4

In my case run Visual Studio as administrator helped. My project uses local IIS and Studio needs Admin permissions to manage IIS.

Answer 5

I encountered the

The Extender Provider failed to return an Extender for this object.

message in a winforms designer window.

I'm aware that your question is about ASP.Net 3.5, but in my case I resolved it by:

• Closing the solution in Visual Studio
• Deleting the obj and bin directories from the problematic project.

When I reopened the solution the error no longer occurred in the designer.

Answer 6

For me none of the solutions above worked. I am using VS 2019. In my case, the repository had special characters in the name, so when cloned, the root folder had escaped characters in the name. The compiler could no longer match the file names. Updating the parent folder name and reopening VS fixed the issue.

The detailed error behind 'Extender Provider failed to return an Extender' was related to the inability to find the compiler targets in the path.