Element 'UpdatePanel' is not a known element

Question

I have one master page in project. I added scripmanager in that page. In one aspx page I added only update panel control because script manager is in master page.I open both file of master page and save. Still I am getting an error Element 'UpdatePanel' is not a known element.

Answer 1

Found this here

Basically quit VS2010, delete the content of your 'Reflected Schema Cache', which should be in something like this:

C:\Users\[Your Username]\AppData\Roaming\Microsoft\VisualStudio\10.0\ReflectedSchemas

Restart VS and you should have fixed it.

Answer 2

I had similar issue and I figured that if we have UpdatePanel under "div" or "span" or even "asp:Content" the VS intellisense doesn't complain. Its strange though.

Answer 3

I was experiencing the same problem and also tried to drag and drop from the toolbox to no avail. I finally was able to solve it by adding the targetFramework="4.0" attribute to my compilation tag in my web.config file.