If you are getting an error like the one below then ASP.NET then checkout http://www.groupsrv.com/dotnet/about147910.html
If the site has been published and has been marked as updateable and you have a class in the application named login then it can result in the error below, the simplest resolution is to rename your class.
Cannot convert type 'ASP.login_aspx' to 'System.Web.UI.WebControls.Login'
Event Type: Warning Event Source: ASP.NET 2.0.50727.0 Event Category: Web Event Event ID: 1310 Date: 11/7/2005 Time: 10:43:16 AM User: N/A Computer: DEVPC01 Description: Event code: 3007 Event message: A compilation error has occurred. Event time: 11/7/2005 10:43:16 AM Event time (UTC): 11/7/2005 4:43:16 PM Event ID: 6c82372492fa42dbbbd4a0f5b794ed8d Event sequence: 40 Event occurrence: 7 Event detail code: 0
Exception information: Exception type: HttpCompileException Exception message: c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\deleted\3ee2c232\4383868\App_Web_login.aspx.cdcab7d2.pfd6ysg8.0.cs(118): error CS0030: Cannot convert type 'ASP.login_aspx' to 'System.Web.UI.WebControls.Login'