Element "UpdatePanel" is not a known element

Question

I have one main page in the project. I have added scripmanager to this page. On one aspx page, I added only the update panel control because the script manager is on the main page. I open both files of the main page and save. However, I get an error. The "UpdatePanel" element is not a known element.

Answer 1

Found here here

Basically close VS2010, delete the contents of your "Reflected Schema Cache", which should be something like this:

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

Reboot VS and you should fix it.

Answer 2

I had a similar problem, and I thought that if we have an UpdatePanel under "div" or "span" or even "asp: Content", VS intellisense does not complain. Strange, however.

Answer 3

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

Answer 4

Put the following code in your web configuration. Just change the assembly to suit your Ajaxtoolkit

 <pages> <controls> <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/> <add namespace="AjaxControlToolkit" assembly="AjaxControlToolkit" tagPrefix="ajaxToolkit"/> </controls> </pages> 

Answer 5

This is one way to resolve the 'UpdatePanel' element is not a known element error if you are using VS2008 or targeting previous frameworks.

You need to explicitly include the following controls / namespaces in the section of web.config pages contained in the system.web file.

 <pages> <controls> <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> <add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/> </controls> </pages> 

Answer 6

 <%@ Register Tagprefix="asp" Namespace="System.Web.UI" Assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" %> 

I was getting this error in VS 2015 due to a link to 3.5 in the System.Web.Extensions directive. Make sure it is 4.0

Answer 7

There was the same problem when I changed from the older .Net to the later .NET 4. Also changed to XHTML5. XHTML5 does not allow use that affects parsing, which causes an error / warning. As soon as I replaced him, he stopped the warnings.

Answer 8

I tried using VS2010:

Basically close VS2010, delete the contents of your Reflected Schema Cache , which should be something like this:

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

Reboot VS and you should fix it.