We all know that App_Code folder contains source code files written as traditional class files — that is, files with a .vb extension, .cs extension, and so on.
But when we keep .cs and .vb file together in one folder and try to build the project it throws errors. So to successfully build the project we follow two simple steps .
Step#1 : Create two folders VBCode for .vb files and CSCode for .cs files.
Step#2: Modify web.config file.
<compilation>
<codeSubDirectories>
<add directoryName=”CSCode”/>
<add directoryName=”VBCode”/>
</codeSubDirectories>
</compilation>
That’s all, Hope this helps.
Enjoy !! 
Salviashish Hi,
I have a project need to run both CS and VB and the compilation goes fine according to your guidelines.
My problem is that I am from a UserControl normally use this call: WebEditor(“Telerik.Samples.LinksListItemEditor, App_Code”) and it does not work.
Do you know how to perform this reference correct to CSCode?
Best regards
Bo
Hi Bo,
I think If you set the compilation property and define compilers for CS or VB in web.config,
It should work. You can refer this http://msdn.microsoft.com/en-us/library/s10awwz0.aspx
Thanks,
Ashish