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

I solved it by just closing Visual Studio and opening it again. I was using Visual Studio 2015 Community Edition and didn't have to delete those folders.

Answer 2

In my case I had deleted 'SSL' from the VS2017 C# project properties debug configuration build tab Conditional compilation symbols. Putting it back resolved the error. Apparently SSL require in Debug configuration (but not release).

Answer 3

I had this issue in Visual Studio 2015, the error kept persisting even after cleaning the project, restarting visual studio and restarting my pc.

What resolved it for me, was right-clicking the xaml file and choosing Open with... > XML Editor. It opened the file and the error didn't occur after that.

Answer 4

None of the solutions above worked in VS2019 for me. What did work was deleting the ProjectName.csproj.user file and then reloading the project.