Why can’t I Publish web site error warn ?

Question

Previously the program was written on VS2005, now I use VS2010 to run the program normally but when I publish the web site I get an error:

It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.

error CS0433: The type 'webapp4U.UI.Controls.Controls_MenuLeft' exists in both 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\nhadat\42a77785\d1e96df3\App_Web_danhmucbds.ascx.cc671b29.dll' and 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\nhadat\42a77785\d1e96df3\App_Web_quangcaoleft.ascx.cc671b29.dll'... 

 

How to fix this error ?